Nakamoto: New stacks-node entry point

[kantai]

A new entry point for stacks-node (switched into via main.rs) for
nakamoto operation. This entry point is responsible for spawning threads
and initializing communication channels.

This entry point should:

1. Start a relayer thread
2. Start a network thread (i.e., the current p2p thread but with the p2p stack disabled)
3. Start a nakamoto coordinator thread
4. Either spawn threading necessary for handling communication channels or loop on comms channels directly

[jcnelson]

Do we have to keep the old Neon node around? Can we instead just create a top-level crate stacks-nakamoto-node or some such and build the node daemon from there?

[saralab]

Closing, merged as part of #3933