Changelog

1. v1 --> v2
2. rpc ReceiveMessage(ReceiveMessageRequest) returns (stream ReceiveMessageResponse) {}
3. Removed Nack RPC to honor ChangeInvisibleDuration RPC in consistent way;
4. SendMessageRequest supports repeated messages; Corresponding response syncs with repeated SendReceipts
5. rpc Telemetry(stream TelemetryCommand) returns (stream TelemetryCommand) {}
6. Removed ProducerGroup;
7. FIFO flags moved from HeartbeatRequest to ConsumerData
8. Removed MessageModel enumeration as concept of broadcasting is totally deprecated;
9. Enums field number = 0 is redefined to meet requirement Each enum value should end with a semicolon, not a comma. Prefer prefixing enum values instead of surrounding them in an enclosing message. The zero value enum should have the suffix UNSPECIFIED.
10. Nested enumerations are externalized due to the same guide item as above.

Remaining Issues: How server publishes conf and conf changes to clients.