ProtobufMetadataManagerInterceptor invokes commands synchronously

ProtobufMetadataManagerInterceptor uses AsyncInterceptorChain.invoke() to invoke lock/put/remove commands. invoke() is synchronous and it will block the thread, so the interceptor should use AsyncInterceptorChain.invokeAsync() instead.

Note that the commands are only invoked only on the originator, so the blocked threads will be from the server's worker thread pool, not from the remote or JGroups thread pools.