Add support for tagging failures in dashboard

[will-cromar]

It would be great if we could tag failures with causes such as infrastructure flakiness, model regressions, or erroneous test configs. It may also be useful to link to bugs or github issues. This would be useful both for record-keeping (e.g. tracking flakiness over time) and to communicate with teammates if an error has been triaged.

[zcain117]

This would be manual tagging right?

Would be awesome to automate somehow but manual seems closer to becoming a reality in the foreseeable future

[will-cromar]

I meant manual tagging, but automatic tagging (e.g. for known flaky failures) would also be great.