feat(git): new `.git:merge-to` job template to merge a reference

By default, the source of the merge is ${CI_COMMIT_TAG} and the target must be defined by the .gitlab-ci.yml job using this template.

• docs/GETTING-STARTED.md: new section to document .git:merge-to template job.

• templates/Git.yaml: new .git:merge-to template job to merge a reference into a target branch.

Closes #6 (closed)

marked this merge request as ready

assigned to @lgourvenec

assigned to @pcaseiro and unassigned @lgourvenec

merged

mentioned in commit bd43ccc9