Support filtering execution metadata by category with any value

It would be useful to query test results and test executions that have a particular category of execution metadata, and any value.

Alternatively, does this just indicate that we are publishing the wrong execution metadata, or that we should publish additional execution metadata that makes this unnecessary?

What about attachment rules though? Should they support the wild card?

No files, tests, or entry points are named. Start by tracing how execution metadata and attachment rules are queried, then clarify whether category-only filtering and wildcard attachment matching are required; done means the agreed behavior is implemented and covered by tests.

Written by the indexing model from the issue text.