feat: distributed via raft

[jdockerty]

TODO

• Place behind a feature of distributed or raft so the functionality is split up nicely.
• impl RaftNetwork/RaftNetworkFactory

Notes

raft-rs vs openraft

I initially started with raft-rs, but have found the documentation to be quite lacking and difficult to understand how to use the library itself. It's obvious that it only provides the consensus module of Raft and the user of the library is expected to provide the storage and transport layers; however, a decent example on how to do this is not present and using tikv as a guide felt impractical to me after awhile or trawling through the code base.

In search for an alternative I've found openraft, which also has a lot of community activity and the documentation goes through a full setup which I'm now looking to implement in this PR.

[jdockerty]

Closing for now.

This is superseded by some basic replication strategy and raft/more complicated distributed models can be visited at a later date.