tor-hsservice: Implement PartialEq for HsClientDescEncKey, Anonimity, DescEncryptionConfig

This will enable the descriptor publisher to tell whether it needs to update the descriptor.

When the publisher is notified of an OnionServiceConfig change, it checks whether the anonimity or encrypt_descriptor fields have changed. If they have, it rebuilds and republishes the descriptor using the new values (note: the publisher changes will be implemented in a future commit).