[APIView] Block PRs from being merged in GitHub

With swagger/Cadl support coming online for APIView, I feel one important feature that's needed is to somehow block PRs on GitHub from being merged while there are unresolved comments. Ideally, showing those comments on appropriate lines in the PR would be nice so we're not forced to use separate tools- GitHub and APIView - but perhaps consider that a stretch or I can open another issue.

At the very least, perhaps some sort of hook to prevent merging while there are unresolved comments. I assume links will still be added to PRs so that service teams know to look at APIView, but randomized assignees for merging need to know why a PR is blocked and not be able to override e.g., a required check.

The issue identifies APIView and GitHub but does not name files, tests, or an entry point. Start by locating APIView's existing pull-request integration and the repository's GitHub checks or merge-control configuration; completion would require an agreed design for blocking merges when APIView comments remain unresolved.

Written by the indexing model from the issue text.