deploy_gitlab_ci: integrate only correct projects into the manifest
Previously we integrated all projects into the manifest, even those that
belonged to a different manifest branch. That led to all manifests
having the same project revisions, even if they should be different due
to different intgrated project branches.
Save a list of integration sources for each manifest branch separately
now, so that we can check which project belongs to which manifest branch
later.
When we're integrating a single branch into a single manifest branch,
there is no need to run the intgeration pipeline for all configured
integrations, but only for those that match the target branch of the
current merge request.
