AI:
- add dimensions_flat to TaskResultSummary and index it.
- create new API for the user to select between 'search by tag' or 'search by dimensions'.

In practice I'm still not convinced it's worth the work, as users would have an hard time selecting the right tag, and there's UX challenges to surface this correctly.

The rationale for this issue is recipes misbehaving in the tags they are submitting. It think it's better hygiene to fix the recipe to specify useful tags. This is better from a monitoring purpose.

The more I think about it, the less I think it's a good idea, because this incite users to keep anti-patterns; messy tags. So I'll close it.