Add customer's hooks to client / server ends

[abukharov268]

• Add configurable options to add hook functions to filter or mutate inbound / outbound messages on WebSocket channels:
  • Client callbacks (topic, message, data):
    • BeforeMessageSent
    • AfterMessageReceived
  • Server:
    • BeforeMessageSent (before the pipeline)
    • AfterMessageReceived (after the pipeline)
• Use OmegaConf
• Consider what naming to use
• Consider what signature to use. Take into account that the customer may not use IDE to write to hooks. So the signature should probable avoid relying on complex typing
  • For example __call__(topic: str, m: Message, payload: bytes) -> Optional[Tuple(str, Message, bytes)]
• Add corresponding docs