Implement v6 Leasequery in Leasequery hook library

This issue builds upon #978 (closed) which created the LeaseQuery hook library and implemented DHCP V4 LeaseQuery (per RFC 4388) and create the v6 implementation stubs. Originally #978 (closed) was to provide both, we split the effort so V4 can roll out first. This issue fills in the v6 Leasequery implementation.

Edited May 22, 2020 by Thomas Markwalder

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