Enable STL-ASAN-CI on PRs

[CaseyCarter]

.... but set the UI to require a maintainer comment to trigger.

[CaseyCarter]

/azp run STL-ASan-CI

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[CaseyCarter]

If and when we merge this change, we need to update the Wiki page that describes how to recreate the pipelines: there's a manual UI step needed to require a maintainer comment before running a pipeline. Without that setting, STL-ASan-CI will now run automatically on all PRs.

As far as a can tell, there's no way to do this purely in YAML - which is why I didn't do so previously. I think the value of triggering the optional pipeline outweighs the annoyance of hand configuration. It's annoying to PR an ASan fix with no way to run the CI before merging.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for improving the ASAN experience! 📈 🎉 😸

[CaseyCarter]

If and when we merge this change, we need to update the Wiki page that describes how to recreate the pipelines: there's a manual UI step needed to require a maintainer comment before running a pipeline. Without that setting, STL-ASan-CI will now run automatically on all PRs.

I have updated the Wiki instructions.