Configuration - decide fate and form of 'Category'

Blocked by https://github.com/dotnet/msbuild/issues/9823 (that item will decide the fate and possibly resolve this)

### Context

Initial proposal of `BuildAnalyzerRule` has a `Category` field:

https://github.com/dotnet/msbuild/blob/5fab936eeb1a112eb4fb3e611818d33d70238903/src/Build/BuildCheck/API/BuildAnalyzerRule.cs#L46-L49

However it was not yet decided how that will be used and if that should be a freeform text or fixed enum.

### Goals
* Decide whether we should bring back the `Category` and what would be the usage for the field (e.g. mass-configuration of rules by customer, or improved UX)
* If decided that it's needed:
* Document the usage and expected configuration by custom Checks authors
* Reintroduce to code

### Possibly related

https://github.com/dotnet/msbuild/issues/9823