Bridges V2 refactoring backport and `pallet_bridge_messages` simplifications (#4935)

## Summary

This PR contains migrated code from the Bridges V2
[branch](https://github.com/paritytech/polkadot-sdk/pull/4427) from the
old `parity-bridges-common`
[repo](https://github.com/paritytech/parity-bridges-common/tree/bridges-v2).
Even though the PR looks large, it does not (or should not) contain any
significant changes (also not relevant for audit).
This PR is a requirement for permissionless lanes, as they were
implemented on top of these changes.

## TODO

- [x] generate fresh weights for BridgeHubs
- [x] run `polkadot-fellows` bridges zombienet tests with actual runtime
1.2.5. or 1.2.6 to check compatibility
-  working, checked with 1.2.8 fellows BridgeHubs
- [x] run `polkadot-sdk` bridges zombienet tests
  -  with old relayer in CI (1.6.5) 
- [x] run `polkadot-sdk` bridges zombienet tests (locally) - with the
relayer based on this branch -
https://github.com/par...