Single approved signer registry

[yondonfu]

Orchestrators and broadcaster can use a single registry to approve/revoke signers that sign off-chain data on behalf of their main ETH account. Any contract that supports approved signers should be aware of this registry and during signature validation should:

• Check if the recovered address from a signature matches the provided address
• If not, check if the recovered address is an approved signer in the registry for the provided address