Invoke post-receive hook after transaction commit

post-receive hook is currently invoked by the RPC handler. With transactions this means that the post-receive hook is invoked before the transaction commits which happens after the handler has finished. This can trigger CI execution and other processes before the write is available through the API. To avoid this, we should execute the post-receive hook only after the transaction has committed.

Related issue in Praefect: #5406 (closed)