housekeeping: Add housekeeping middleware

#5709

This MR adds HousekeepingMiddleware which intercepts gRPC requests, independent of whether transactions are enabled. The scheduler:

• decides whether to invoke OptimizeRepository based on a configurable housekeeping interval.
• ensures only a single OptimizeRepository job is executing concurrently.

The middleware is guarded behind a new feature flag in case it results in performance degradation. If the middleware encounters errors, they are logged and the handler is invoked immediately, short-circuiting the middleware logic.