CI: Deploy: create integration branches and trigger pipelines in subprojects

Allow deploy_gitlab_ci to change multiple projects at once.
Use it to create integration branches and merge requests in all
projects.

Add a python file to generate a job yml from jinja2 template.
Add a template for the jobs to trigger. These execute the actual
integration in all 'subprojects'.
Create the yml file in the deploy job and trigger it in a new trigger
job.