minikv (v2.0.0)

Release v2.0.0: rework the distributed layer

- Raft: persistent log and term, elections with log up-to-date checks, majority commit, ReadIndex for linearizable reads
- Writes: 2PC between coordinators and volume servers, metadata replicated through Raft, versioned blobs
- Volume server: gRPC storage service, health endpoint, heartbeats
- End-to-end test: 3 coordinators + 3 volumes with leader failover
- Makefile: make ci mirrors the CI, make smoke runs the cluster test, scripts run through bash
- Docs: README, CONTRIBUTING, LEARNING, RAM_COMMUNITY and CHANGELOG updated for v2.0.0