refactor notification protocols

[turuslan]

Referenced issues

Description of the Change

• peer count metric and telemetry count "/announce" streams, not connections.
• protocols are independent.
  • but "/announce" protocol controls "/grandpa" and "/transaction" protocols.
  • authority discovery controls "/validation" protocol.
• protocol error doesn't close connection to peer, only that protocol stream.
• protocols decide when to open streams.
• "/collation" and "/validation" protocols handle ViewUpdate messages, delegating other messages to observer.

Possible Drawbacks

• check peer reputation before connecting (how can peer reputation grow if there are no streams to raise reputation?)