[AVC] Support namespace review

Add an endpoint to allow AVC to review just the namespace for an APIView. This would be a narrow set of guidelines and a short prompt.

Per Ted:
"Even just asking it whether the package name matches the guidelines per language would help. We always see people trying to sneak in a two level namespace or not use one of the existing groups."

Start by locating AVC's existing APIView review endpoints and the language-specific namespace guidelines they use. Determine where a namespace-only review request and its short prompt belong, then verify that the endpoint evaluates package names against the permitted namespace groups and language rules.

Written by the indexing model from the issue text.