Integrate HA hook into base code
There were two original reasons to have HA implemented as a hook: we wanted it to be optional, so people not interested wouldn't run the code and the second was business. Neither of those aged well and it is now more of a burden to maintain and extend HA.
As such, @marcin proposed to integrate the code into core Kea. This is a master-ticket covering this goal. If needed, feel free to create additional ticket(s) for design or split this into smaller tasks.