Configurable RC/GA branch names

[bonndan]

We are evaluating braumeister im combination with gitlab. Aside from that our current branch naming habits are different, we also have to use regexes to control our branch-based gitlab pipelines. For instance:

deploy_dev:
  ...
  only:
    - /^release\/*_RC_*$/

would be required to trigger an RC pipeline. I never get regexes right at the first try 😄 and I'd say it's error prone.

One useful feature might be to make the generated branch names more configurable, e.g. that RC simpy start with "rc_" if I want and similarly for GA branches.