Create new release when merge requests are merged into the
`$STABLE_BRANCH` branch.

* templates/Release/Semantic-release.yaml: run `semantic-release` with
  the latest EOLE container for `$STABLE_BRANCH` branch if one of its
  configuration is present.

* .gitlab-ci.yml: execute a new stage `release` for
  `semantic-release`.

* release.config.js: create `docs/CHANGELOG.md` and publish new
  releases on Gitlab.
  Mangle commits to have links for users, issues and commits id.

* release-rules.js: create semantic version update rules based on
  `docs/CONTRIBUTING.md`.

This will permit other projects to
[include](https://docs.gitlab.com/ee/ci/yaml/#include) the defined
templates

The `templates/Rules.yaml` must be included and jobs will `extends`
the templates depending at which moment they must be executed.

* .gitlab-ci.yml: define only stage `lint` for now and run
`commitlint` at that stage.

* docs/CONTRIBUTING.md: describe the commit message formatting rules.

* README.md: link to the contributing guide.