Dynamical job creation for multiple DSID commits

When we run athena the job will check if the expected time is > 1h and will abort if it is. If several DSIDs are added simultaneously (e.g. 10-30 DSIDs for SUSY, EXO signal grids) the run_athena job will run for a very long time.

We should find a workaround for that. Could be handled with the commit_new_dsid.sh script making several branches.

Some interesting material here: https://gitlab.com/gitlab-org/gitlab-ce/issues/45828

In particular there's a feature request for dynamic CI jobs: https://gitlab.com/gitlab-org/gitlab-ce/issues/44199 probably to be implemented in early 2020.

Update: this seems to be exactly what we need: https://gitlab.com/gitlab-org/gitlab/issues/35632