Split out cluster membership into separate module

[ChillFish8]

Currently the chitchat membership, RCP layer and node selector are embedded within the cluster repo.

We want to split this out into a dedicated datacake-node crate and rename the existing datacake-cluster crate to be datacake-eventually-consistent to better reflect the functionality.

The motivation for this is that the membership and management can be the base building block that we can efficiently extend with these additional crates, current that would just be via the eventually consistent crate, but we want to support multi-raft and extending on that, be prepared.