Complete fix of 5.4 Reshare Denial-of-Service via Predicable Instance IDs

[pavelkrolevets]

• compute instance ID at operators as `[24]byte = [8]byte(keccak(initiator pub)) + [8]byte(keccak(message)) + [8]byte(uuid entropy)

This effectively prevents malicious actors to create same instance IDs at operators for DoS as [8]byte of keccak(initiator pub) ensures that only initiator can use one unique ID as we verify his signature and ensure that pub key belongs to initiator.

[MatusKysel]

LGTM