Organize coordinator group

[as51340]

This PR creates RAFT cluster of coordinators which all know about each other. We remove --coordinator flag and add --raft-server-id and -raft-server-port flag in order to correctly initialize raft servers. Added ADD COORDINATOR query for connecting instances. Coordinators know about each other and can get info about the cluster state using SHOW INSTANCES. ATM CoordinatorLogStore, CoordinatorStateMachine and CoordinatorStateManager don't do anything too smart but they will in the future.

[master < Epic] PR

• Check, and update documentation if necessary
• Write E2E tests
• Compare the benchmarking results between the master branch and the Epic branch
• Provide the full content or a guide for the final git message

[master < Task] PR

• Check, and update documentation if necessary
• Provide the full content or a guide for the final git message

To keep docs changelog up to date, one more thing to do:

• Write a release note here, including added/changed clauses
• Tag someone from docs team in the comments

[antoniofilipovic]

Good work, not much to comment 💪

[andrejtonev]

Looks good!
A few comments.
Didn't get into the raft stuff. I'll need a sync for that :D

[as51340]

@kgolubic release note: Added flags --raft-server-id and --raft-server-port for creating coordinators.