Support GitHub Enterprise (GKDev) in Launchpad

[sergeibbb]

This is a follow-up of #3901, where we have started supporting GitHub Enterprise integrations from GKDev. We show autolinks on issues and pull-requests and show PRs on branches and commits.

Now we want to show theirs PRs in our Launchpad.

Testing notes

• We need to test with a PR that is failing CI, and ensure that the new statusCheckRollup field actually works (both on GitHub.com and on Enterprise)

Follow ups

#3934