In scope

• Upgrade to github branch source 1.8 https://github.com/jenkinsci/github-branch-source-plugin/commit/949791b2c99fcfffab1899975350ce0fb1600e26

Notes
Currently, all branches are built in a multibranch pipeline project. When a pull request is opened from one branch to master, Jenkins doesn't pick this up as a new build (as it has already built the branch).

Blue ocean however NEEDS to present this as a PR. Not clear how or where to solve this. When a PR is opened that is a human event implying that attention is now needed, however, with multibranch, no build should be triggered (as it already would have been with the branch).

Perhaps blue ocean needs to note that a given branch also has a PR open and present it differently (but doesn't explain how it will live-update the UI when PR is opened, but perhaps that is a ticket for another day...)