CI can't merge tag release in `dev`

Merging the release tag is rarely a fast forward of dev branch. When the released is prepared, new commits contribution could be merged in dev.

This requires a merge commit and git requires name and email for authoring it.

Gitlab-ci does not export the git authoring variables:

• $GIT_AUTHOR_NAME
• $GIT_AUTHOR_EMAIL
• $GIT_COMMITTER_NAME
• $GIT_COMMITTER_EMAIL

We need to extract the information either from $CI_COMMIT_AUTHOR containing NAME <EMAIL>, or from $GITLAB_USER_NAME and $GITLAB_USER_EMAIL.