Switch from bors to merge queue

The publicly hosted instance of bors-ng is deprecated. Therefore we switch to GitHub merge queue.

Two things are happening:

This PR edits config files to switch from bors to the new github merge queue.
Additionally the repository settings and in particular the branch protection rules are edited as described in the docs.

I am a bit unsure how to test this without creating a huge amount of pull requests, but I hope the changed settings already take effect for this PR.

knurling-rs / probe-run