Investigate Github branch source plugin for Submarine PR checks

PR automation needs to be prepared for the Submarine initiative repositories. There is a suggestion from manaRH to take a look at Github Branch Source plugin [1] as it should be the recommended way how to do this.

Deliverables:

• PR automation proof of concept for the submarine engines repository.

[1] https://go.cloudbees.com/docs/plugins/github-branch-source/