JackalBridge: Optimize Relayer Check to Reduce Gas Cost

[fintechup]

Description:
Currently, every message settlement verifies whether msg.sender is the owner or a relayer by looping through the relays array. This increases gas costs, especially when there are many relayers.

To optimize this, introduce a mapping(address => bool) isRelayer and use it for checks instead. This will eliminate the need for iteration and reduce gas consumption.

[solophbs]

I'm not sure if this has already been addressed, but if not, I would recommend using AddressSet from OpenZeppelin. It can help manage addresses more efficiently and securely.
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/structs/EnumerableSet.sol#L306