feat: add extra release tags

| `skopeo-image` / `CNB_SKOPEO_IMAGE` | The Docker image used to run [skopeo](https://github.com/containers/skopeo) | `quay.io/containers/skopeo:latest` <br/>[![Trivy Badge](https://to-be-continuous.gitlab.io/doc/secu/trivy-badge-CNB_SKOPEO_IMAGE.svg)](https://to-be-continuous.gitlab.io/doc/secu/trivy-CNB_SKOPEO_IMAGE) |

| `publish-args` / `CNB_PUBLISH_ARGS` | Additional [`skopeo copy` arguments](https://github.com/containers/skopeo/blob/master/docs/skopeo-copy.1.md#options) | _(none)_          |

| `prod-publish-strategy` / `CNB_PROD_PUBLISH_STRATEGY` | Defines the publish to production strategy. One of `manual` (i.e. _one-click_), `auto` or `none` (disabled). | `manual` |

| `release-extra-tags-pattern` / `CNB_RELEASE_EXTRA_TAGS_PATTERN` | Defines the image tag pattern that `$CNB_RELEASE_IMAGE` should match to push extra tags (supports capturing groups - [see below](#using-extra-tags)) | `^v?(?P<major>[0-9]+)\\.(?P<minor>[0-9]+)\\.(?P<patch>[0-9]+)(?P<suffix>(?P<prerelease>-[0-9A-Za-z-\\.]+)?(?P<build>\\+[0-9A-Za-z-\\.]+)?)$` _(SemVer pattern)_ |

| `release-extra-tags` / `CNB_RELEASE_EXTRA_TAGS`                 | Defines extra tags to publish the _release_ image (supports capturing group references from `$CNB_RELEASE_EXTRA_TAGS_PATTERN` - [see below](#using-extra-tags)) | _(none)_ |

This job produces _output variables_ that are propagated to downstream jobs (using [dotenv artifacts](https://docs.gitlab.com/ci/yaml/artifacts_reports/#artifactsreportsdotenv)):

| `cnb_digest`       | release image digest                                  | `sha256:b7914a91...`                    |

They may be freely used in downstream jobs (for instance to deploy the upstream built image, whatever the branch or tag).

#### Using extra tags

When publishing the _release_ image, the Docker template might publish it again with additional tags (aliases):

- the original published image tag (extracted from `$CNB_RELEASE_IMAGE`) must match `$CNB_RELEASE_EXTRA_TAGS_PATTERN` ([semantic versioning](https://semver.org/) pattern by default),

- extra tags to publish can be defined in the `$CNB_RELEASE_EXTRA_TAGS` variable, each separated with a whitespace.

:information_source: the Docker template supports [group references substitution](https://learnbyexample.github.io/py_regular_expressions/groupings-and-backreferences.html) to evaluate extra tags:

- `$CNB_RELEASE_EXTRA_TAGS_PATTERN` supports capturing groups:

  - `v([0-9]+)\.([0-9]+)\.([0-9]+)` has 3 (unnamed) capturing groups, each capturing any number of digits

  - `v(?<major>[0-9]+)\.(?<minor>[0-9]+)\.(?<patch>[0-9]+)` has 3 **named** capturing groups (_major_, _minor_ and _patch_), each capturing any number of digits

- `$CNB_RELEASE_EXTRA_TAGS` supports capturing group references from `$CNB_RELEASE_EXTRA_TAGS_PATTERN`:

  - `\g1` is a reference to capturing group number 1

  - `\g<major>` is a reference to capturing group named _major_

:information_source: the default value of `$CNB_RELEASE_EXTRA_TAGS_PATTERN` matches and captures all parts of a standard [semantic versioning](https://semver.org/)-compliant tag:

- the **major** group captures the major version

- the **minor** group captures the minor version

- the **patch** group captures the patch version

- the **prerelease** group captures the (optional) pre-release version (including the leading `-`)

- the **build** group captures the (optional) build version (including the leading `+`)

- the **suffix** group captures the (optional) entire suffix (including pre-release and/or build)

Example: publish latest, major.minor and major aliases for a SemVer release:

```yaml

variables:

  # ⚠ don't forget to escape backslash character in yaml

  CNB_RELEASE_EXTRA_TAGS: "latest \\g<major>.\\g<minor>\\g<build> \\g<major>\\g<build>"

```

With this contiguration, the following extra tags would be published:

| original tag           | extra tags                                                  |

| ---------------------- | ----------------------------------------------------------- |

| `main`                 | _none_ (doesn't match `$CNB_RELEASE_EXTRA_TAGS_PATTERN`)    |

| `some-manual-tag`      | _none_ (doesn't match `$CNB_RELEASE_EXTRA_TAGS_PATTERN`)    |

| `1.2.3`                | `latest`, `1.2`, `1`                                        |

| `1.2.3-alpha.12`       | `latest`, `1.2`, `1`                                        |

| `1.2.3+linux`          | `latest`, `1.2+linux`, `1+linux`                            |

| `1.2.3-alpha.12+linux` | `latest`, `1.2+linux`, `1+linux`                            |

      "description": "CNB snapshot image",

      "default": "$CI_REGISTRY_IMAGE/snapshot:$CI_COMMIT_REF_SLUG"

    },

    {

      "name": "CNB_RELEASE_EXTRA_TAGS_PATTERN",

      "description": "Defines the image tag pattern that `$CNB_RELEASE_IMAGE` should match to push extra tags (supports capturing groups)\n\nDefaults to [SemVer](https://semver.org/) pattern.",

      "default": "^v?(?P<major>[0-9]+)\\.(?P<minor>[0-9]+)\\.(?P<patch>[0-9]+)(?P<suffix>(?P<prerelease>-[0-9A-Za-z-\\.]+)?(?P<build>\\+[0-9A-Za-z-\\.]+)?)$",

      "advanced": true

    },

    {

      "name": "CNB_RELEASE_EXTRA_TAGS",

      "description": "Defines extra tags to publish the _release_ image\n\nSupports capturing group references from `$CNB_RELEASE_EXTRA_TAGS_PATTERN` (ex: `latest \\g<major>.\\g<minor> \\g<major>`)",

      "advanced": true

    },

    {

      "name": "CNB_RELEASE_IMAGE",

      "description": "CNB release image",

    release-image:

      description: CNB release image

      default: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME

    release-extra-tags-pattern:

      description: |-

        Defines the image tag pattern that `$CNB_RELEASE_IMAGE` should match to push extra tags (supports capturing groups)

        Defaults to [SemVer](https://semver.org/) pattern.

      default: ^v?(?P<major>[0-9]+)\.(?P<minor>[0-9]+)\.(?P<patch>[0-9]+)(?P<suffix>(?P<prerelease>-[0-9A-Za-z-\.]+)?(?P<build>\+[0-9A-Za-z-\.]+)?)$

    release-extra-tags:

      description: |-

        Defines extra tags to publish the _release_ image

        Supports capturing group references from `$CNB_RELEASE_EXTRA_TAGS_PATTERN` (ex: `latest \g<major>.\g<minor> \g<major>`)

      default: ''

    skopeo-image:

      description: The docker image used to publish docker image with Skopeo

      default: quay.io/containers/skopeo:latest

  # default: one-click publish

  CNB_PROD_PUBLISH_STRATEGY: $[[ inputs.prod-publish-strategy ]]

  CNB_RELEASE_EXTRA_TAGS_PATTERN: $[[ inputs.release-extra-tags-pattern ]]

  CNB_RELEASE_EXTRA_TAGS: $[[ inputs.release-extra-tags ]]

  CNB_PUBLISH_ARGS: $[[ inputs.publish-args ]]

  # default trivy

    fi

  }

  function maybe_install_python3() {

    if ! command -v python3 > /dev/null

    then

      if command -v apt-get > /dev/null

      then

        # Debian

        apt-get update

        apt-get install --no-install-recommends --yes --quiet python3

      elif command -v apk > /dev/null

      then

        # Alpine

        apk add --no-cache python3

      elif command -v dnf > /dev/null

      then 

        # Fedora

        dnf install -y -q python3

      else

        log_error "... didn't find any supported package manager to install python3"

        exit 1

      fi

    fi

  }

  function unscope_variables() {

    _scoped_vars=$(env | awk -F '=' "/^scoped__[a-zA-Z0-9_]+=/ {print \$1}" | sort)

    if [[ -z "$_scoped_vars" ]]; then return; fi

    rm -f "${FIND_PATTERNS_FILE}"

  }

  function publish_extra_tags() {

    if [[ -z "$CNB_RELEASE_EXTRA_TAGS" ]]

    then

      return

    fi

    # check if tag matches pattern

    maybe_install_python3

    # shellcheck disable=SC2154

    matches=$(python3 -c "import re;print('match' if re.match(r'$CNB_RELEASE_EXTRA_TAGS_PATTERN', '$cnb_tag') else '')")

    if [[ "$matches" ]]

    then

      # apply extra tags substitution

      extra_tags=$(python3 -c "import re;print(re.sub(r'$CNB_RELEASE_EXTRA_TAGS_PATTERN', r'$CNB_RELEASE_EXTRA_TAGS', '$cnb_tag'))")

      log_info "Pushing extra tags (evaluated from original tag \\e[33;1m${cnb_tag}\\e[0m)..."

      for extra_tag in $extra_tags

      do

        log_info "... pushing extra tag: \\e[33;1m${extra_tag}\\e[0m..."

        # shellcheck disable=SC2086,SC2154

        skopeo copy ${TRACE+--debug} --all --src-authfile ~/.docker/config.json --dest-authfile ~/.docker/release-config.json ${CNB_PUBLISH_ARGS} "docker://$CNB_RELEASE_IMAGE" "docker://$cnb_repository:$extra_tag"

      done

    else

      log_info "Extra tags configured, but the released tag (\\e[33;1m${cnb_tag}\\e[0m) doesn't match \$CNB_RELEASE_EXTRA_TAGS_PATTERN..."

    fi

  }

  # ENDSCRIPT

# job prototype

        echo "cnb_digest=$cnb_digest"

      } > cnb.env

      chmod 644 cnb.env

    - publish_extra_tags

  artifacts:

    reports:

      dotenv: