CI: deploy_gitlab_ci: Rework the deployment of gitlab-ci into the child projects

The deploy_gitlab_ci now creates the integration commit and branch in each passed subproject and create an integration commit in the manifest containing all these new revisions. A build is then triggered on this commit to test the functionality.

Split the update_submodule functions to reuse them in different ways. Remove some previously used files.

BCS 746-000740