node-services protocol is meant for internal restate communication. pb/ appears to go beyond the internal cluster scope.

We need to consolidate a few bits of the system into a core crate to avoid the unnecessary dependency management hassle.

The end goal is to consolidate many of the shared components into this crate. At the moment, task-center and metadata appear to be the best candidate since they are used from everywhere.

as described in the previous PR in the stack

Access to metadata has never been easier. Access `metadata()` by importing `restate_core::metadata`;