Handle 429 errors from POST /internal/allowed via HookService

Context

In !8288 (merged), we modified how errors arising from calling the Rails POST /internal/allowed endpoint were propagated to gRPC middleware. This allowed the majority of hook-based RPCs to report a semantically correct RESOURCE_EXHAUSTED gRPC status code when Gitaly was being rate-limited by Rails.

Proposal

!8288 (comment 2913358702) explains a follow-up fix that's required in order to handle the remaining hook-based RPCs.