docs: update stale links to GitLab docs (anchors)

## Usage

This template can be used both as a [CI/CD component](https://docs.gitlab.com/ee/ci/components/#use-a-component-in-a-cicd-configuration) 

This template can be used both as a [CI/CD component](https://docs.gitlab.com/ee/ci/components/#use-a-component) 

or using the legacy [`include:project`](https://docs.gitlab.com/ee/ci/yaml/index.html#includeproject) syntax.

### Use as a CI/CD component

- [deployment context variables](#deployment-context-variables) provided by the CI/CD template,

- any [GitLab CI variable](https://docs.gitlab.com/ee/ci/variables/predefined_variables.html)

- any [custom variable](https://docs.gitlab.com/ee/ci/variables/#add-a-cicd-variable-to-a-project)

- any [custom variable](https://docs.gitlab.com/ee/ci/variables/#for-a-project)

(ex: ${SECRET_TOKEN} that you have set in your project CI/CD variables)

The deployment context variable `$environment_type` is passed as

The Helmfile template supports two ways of providing your environments url:

* a **static way**: when the environments url can be determined in advance, probably because you're exposing your routes through a DNS you manage,

* a [**dynamic way**](https://docs.gitlab.com/ee/ci/environments/#set-dynamic-environment-urls-after-a-job-finishes): when the url cannot be known before the deployment job is executed.

* a [**dynamic way**](https://docs.gitlab.com/ee/ci/environments/#set-a-dynamic-environment-url): when the url cannot be known before the deployment job is executed.

The **static way** can be implemented simply by setting the appropriate configuration variable(s) depending on the environment (see environments configuration chapters):

Here are some advices about your **secrets** (variables marked with a :lock:):

1. Manage them as [project or group CI/CD variables](https://docs.gitlab.com/ee/ci/variables/#add-a-cicd-variable-to-a-project):

1. Manage them as [project or group CI/CD variables](https://docs.gitlab.com/ee/ci/variables/#for-a-project):

    * [**masked**](https://docs.gitlab.com/ee/ci/variables/#mask-a-cicd-variable) to prevent them from being inadvertently

      displayed in your job logs,

    * [**protected**](https://docs.gitlab.com/ee/ci/variables/#protected-cicd-variables) if you want to secure some secrets