Update ceremony ID length from 24 bytes to 32 bytes

[alan-ssvlabs]

After implementing bulk resign and bulk reshare, ceremony instance IDs stored by the operator are computed as the first 24 bytes of the 32 bytes hash of the resign/reshare message. While it works, it is not the best design. It is better to change the instance ID to 32 bytes but before doing that need to make sure it doesn't break existing things.