docs: normalise table headers

The environment variables are available in the helmfile template with the

`{{ env "<ENV_VAR_NAME>" }}` directive.

| environment variable | template directive | description |

| environment variable | template directive | Description |

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

| `$environment_name`  | `{{ env "environment_name" }}` | a generated application name to use for the current deployment environment (ex: `myproject-review-fix-bug-12` or `myproject-staging`). This should be used as **release name** in the `helmfile.yaml` - _details below_ |

| `$environment_type`  | `{{ env "environment_type" }}` | the current deployment environment type (`review`, `integration`, `staging` or `production`) |

  - name: mycharts

    url: https://repo.example.io/mycharts/stable

releases:

- name: {{ env "environment_name" | default "myapp" }}

- name: {{ env "environment_name" | Default "myapp" }}

  chart: mycharts/webapp

  version: "1.2.0" 

  namespace: {{ .Namespace }}  

The Helm template uses some global configuration used throughout all jobs.

| Name                  | description                            | default value     |

| Name                  | Description                            | Default value     |

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

| `HELMFILE_CLI_IMAGE`      | The Docker image used to run helmfile <br/>:warning: **set the version required by your Kubernetes server** | `ghcr.io/helmfile/helmfile:latest` |

| `HELMFILE_PATH`     | The path to your `helmfile.yaml` | `./helmfile.yaml` |

Here are variables supported to configure review environments:

| Name                         | description                            | default value     |

| Name                         | Description                            | Default value     |

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

| `HELMFILE_REVIEW_ENABLED`    | Set to `true` to enable `review` env   | _none_ (disabled) |

| `HELMFILE_REVIEW_APP_NAME`   | Application name for `review` env      | `"${HELM_BASE_APP_NAME}-${CI_ENVIRONMENT_SLUG}"` (ex: `myproject-review-fix-bug-12`) |

Here are variables supported to configure the integration environment:

| Name                         | description                            | default value     |

| Name                         | Description                            | Default value     |

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

| `HELMFILE_INTEG_ENABLED`     | Set to `true` to enable `integration` env | _none_ (disabled) |

| `HELMFILE_INTEG_APP_NAME`    | Application name for `integration` env | `$HELMFILE_BASE_APP_NAME-integration` |

Here are variables supported to configure the staging environment:

| Name                         | description                            | default value     |

| Name                         | Description                            | Default value     |

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

| `HELMFILE_STAGING_ENABLED`   | Set to `true` to enable `staging` env  | _none_ (disabled) |

| `HELMFILE_STAGING_APP_NAME`  | Application name for `staging` env     | `$HELMFILE_BASE_APP_NAME-staging` |

Here are variables supported to configure the production environment:

| Name                     | description                            | default value     |

| Name                     | Description                            | Default value     |

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

| `HELMFILE_PROD_DISABLED` | Set to `true` to disable `production` env | _none_ (disabled)  |

| `HELMFILE_PROD_APP_NAME` | Application name for `production` env  | `$HELMFILE_BASE_APP_NAME` |

This job runs a [helm lint](https://helm.sh/docs/helm/helm_lint/) across all of the charts/releases in the helmfile manifest and

uses the following variables:

| Name                  | description                               | default value     |

| Name                  | Description                               | Default value     |

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

| `HELMFILE_LINT_ENABLED`   | Set to `true` to enable Helmfile lint | _none_ (disabled) |

| `HELMFILE_LINT_ARGS`      | The helmfile [command with options](https://helmfile.readthedocs.io/en/latest/#lint) to trigger the analysis | `lint` |

It uses the following variables:

| Name                     | description                              | default value     |

| Name                     | Description                              | Default value     |

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

| `HELMFILE_TEST_ENABLED`  | Set to `true` to enable Helm test                 | _none_ (disabled) |

| `HELMFILE_TEST_ARGS`      | The helmfile [command with options](https://helmfile.readthedocs.io/en/latest/#test)

In order to be able to communicate with the Vault server, the variant requires the additional configuration parameters:

| Name              | description                            | default value     |

| Name              | Description                            | Default value     |

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

| `TBC_VAULT_IMAGE` | The [Vault Secrets Provider](https://gitlab.com/to-be-continuous/tools/vault-secrets-provider) image to use (can be overridden) | `$CI_REGISTRY/to-be-continuous/tools/vault-secrets-provider:master` |

| `VAULT_BASE_URL`  | The Vault server base API url          | _none_ |

With:

| Name                             | description                            |

| Name                             | Description                            |

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

| `secret_path` (_path parameter_) | this is your secret location in the Vault server |

| `field` (_query parameter_)      | parameter to access a single basic field from the secret JSON payload |