V6 LeaseQuery by address will not return a delegated prefix which contains query address

The following discussion from https://gitlab.isc.org/isc-private/kea-premium/-/merge_requests/112 should be addressed:

• @fdupont started a discussion:

  The RFC is very loose about this (this explains why you skipped it) but the lease query works with prefix delegation too, for instance:

  Query by IPv6 address -  This query allows a requestor to request
        from a server the bindings for a client that either is bound to
        the address or has been delegated the prefix that contains the
        address.

  Of course even logically you should not assign addresses in a prefix you delegates this raises the question to know if the query is for an address or a prefix. It should have been far clearer / simpler to use a dedicated query type or iaprefix sub option...

  I propose to postpone (i.e. another issue or MR) the prefix support. If you agree create a follower and resolve this thread.