pull requests: consider decentralized approval, document expectations

[suskin]

What problem are you facing?

This issue combines a few different ideas that have come up in recent retrospectives, around how to help pull requests flow through the software development apparatus more effectively.

How could Crossplane help solve your problem?

There are two related but different ideas:

• Use a pull request review model which is closer to what Rook uses. The gist of it is that the maintainers with merge permissions don't necessarily need to do an in-depth line by line review if a Known Qualified Reviewer who does not have merge permissions has already done that. This helps us get more people involved in shepherding pull requests into a mergeable state so that we aren't unnecessarily creating a bottleneck.
• Create a document which explains development team expectations, such as turnaround time for pull requests. This helps us to set expectations and uphold our standards more effectively.

[negz]

I believe we've now added a few more maintainers under our new governance model, which has helped to decentralize approval.

[jbw976]

The expectations for maintainers are captured in https://github.com/crossplane/crossplane/blob/master/GOVERNANCE.md#maintainers for further reading :)