Add the ability to only serve grpc instead of wrapping the json rpc with a grpc server

[evan-forbes]

Instead of wrapping the json rpc, we could simply use a grpc server for the endpoints that node uses.

GetSignedBlockByHeight
GetSignedBlockByHash
subscribe to new SignedBlockEvent

subscription could optionally be implemented on the client side

[rach-id]

The final list of endpoints:

• BlockByHash:
  • Request: block hash
  • Response: block
  • Details:
    • Response to be streamed
• BlockByHeight:
  • Request: block height
  • Response: block
  • Details:
    • Response to be streamed
• Commit:
  • Request: block hash
  • Response: commit
• BlockChunkByHash:
  • Request:
    • hash or height?
    • chunk index
  • Response:
    • chunk
• ValidatorSet:
  • Request: height
  • Response: validator set
• Events subscription:
  • notification of new {height, hash}

ideally, signedblockbyheight endpoint, but that’s a nice to have