Allow maintainers to merge pull requests of committers

[Mic92]

Since we already trust committers to no commit malicious code, we can as well allow maintainers of a package to merge their pull request. This hopefully improves overall reviews because maintainers are often know packages the best and know what to look for.
As this will also remove the workload for committers, this would also improve code quality and reviews in other places.

[pbsds]

This is also a great incentive for co-maintainership