Design and implement raft server and its state for placement

[youngbupark]

In what area(s)?

/area runtime

Describe the feature

This is part of Epic #663

1. Add initial Raft Server implementation.
2. Add DaprHostMemberState State for Raft Finite State Machine.
   • cmd log will construct the list of Dapr runtime member hosts and treat this list as a state. FSM will snapshot this list
3. Consistent hashing table map will be built based on the list of Dapr runtime member hosts; this will not be saved as state.
4. Use MessagePack serialization for state and snapshot.
5. Add three command flags for Raft
   • id: raft node id
   • initial-cluster: raft peer node list - we will not support join option to join new placement node to raft cluster for now.
   • inmem-store-enabled: use in-memory storage for raft log and snapshot (for dev or non-HA mode)
6. Refactor main.go to clean up the code.

Release Note

RELEASE NOTE: ADD Raft server and its state for placement

[youngbupark]

This is to split EPIC #663