Unify the operating mode for bridge pallets

- define the OperationMode trait and BasicOperatingMode enum
- use the OperationMode trait in all the bridge pallets
- use BasicOperatingMode instead of IsHalted for the Grandpa pallet
- use BasicOperatingMode as part of MessagesOperatingMode

Signed-off-by: Serban Iorga <[email protected]>

* store both block number and hash in BestFinalized

* also fix relay code

* spelling

* fix on-different-forks metrics during initialization

* "initialize" parachain finality pallet in on-demand parachains relay

* decrease converstion rate requests count

* more error logging

* fix compilation

* clippy

* introduce FinalityEngine in relay code

* add FinalityEngine to relay

* spelling

* fix test compilation

* Update relays/lib-substrate-relay/src/finality/source.rs

Co-authored-by: Adrian Catangiu <[email protected]>

Co-authored-by: Adrian Catangiu <[email protected]>