Support test coverage analysis when running tests selectively

One other thing that would be great to have with this coverage analysis would be PR impact reports on coverage, so we can see how the changes in a branch affected the coverage of each module it touches (which is very difficult to reason about with selective testing 😅)

we have a dashboard that tracks coverage per module per branch but main is the only one that provides “true” coverage for the whole module since we run tests for the entire module there. prior to selective testing we also had a bot that would hit the metrics server and grab the diff to main and post it as a comment, but that’s useless ever since enabling selective testing.