So far Designate ptr record APIs have been calling Neutron APIs to check
if they match Neutron's floating ips.

That means, for every ptr record API call (including reading-only ones,
such as list and get), Designate was calling Neutron API, removing stale
ptr records, executing other validation and writing-permission operations, and eventually return the result.

If “x-auth-all-projects” HTTP header was provided, Neutron would return an empty list of PTR records.

We do have most of the relevant data in Designate DB tables, such as
records and zones tables. The only missing data is the "stale" ptr records
(that are associated to floating ips that were deleted).

This Epic aims to change ptr record APIs design and implementation, so it will use Designate records & zones DB tables instead of calling neutron APIs.

We could implement additional tasks to get rid of the "stale" ptr records, via producer or sink.