Bridges - add version guarding for standalone relaying of parachains and messages (#5952)

This PR adds the ability to start version guarding when performing
standalone relaying of messages and parachains.

## Follow-up
- decouple and simplify `fn start_relay_guards`:
https://github.com/paritytech/polkadot-sdk/issues/5923

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Co-authored-by: command-bot <>