Add final job for blocking merges of PRs (#7376)

## Summary of changes

Adds a "final" job at the end of ultimate-pipeline that can be used to
block merges

## Reason for change

We have had various cases where the PR had failed, but we merged anyway,
and that broke master. A big reason for that was flakiness, but as we
continue to work on that, we want to make it easy to require a full
green pipeline before merges. Unfortunately, that's a PITA with Azure
DevOps 😅

## Implementation details

- Add two new stages which depend on every other stage, but have
conditions such that they run even if previous stages didn't run
- When those stages run, post the results to GitHub
- Create a job to auto-generate those files (because they're
super-verbose)

## Test coverage

Ran this a few times. Confirmed that if anything fails, this job fails.
If everything passes (or didn't run), this job passes.

## Other details

We can later decide when we want to require this job. Note that we
should _also_ still require _some_ jobs that we expect to always run, to
make sure that things have run that we expect to


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Author: andrewlock