Code monitors: Expose webhooks through GraphQL

Created by: camdencheek

This PR updates the GraphQL layer for code monitors to expose the new webhooks actions.

I apologize for the very large PR. I made multiple attempts to do this incrementally, but kept running into weirdness in the tests that forced me to fix something else, rebase, fix more tests, etc., so I gave up in order to land this so I can keep on track for the quarter. The commits are somewhat incremental, but tests don't pass on each commit due to the above reasons. If someone wants to do a live review, I'm happy to do so if that's easier.