Add support for database-based host reservations

[krocd]

Host reservations reporting seems to only include host reservations included in the config file.

[tomaszmrugalski]

Hey @kevanbrown, ISC's new project stork has support for getting the reservations from both the config file and the database. It's using host_cmds for that. There are more improvements coming up in 0.7.0 (expected on May 6th 2020).

[krocd]

Thank you @tomaszmrugalski for introducing me to Stork. I'll need to get Kea upgraded before I can use it. I'm excited to see that ISC has been working on this type of extremely useful product. I run Kea on Raspbian (now Raspberry Pi OS) and am still on Stretch, so I've had to build the version I'm currently running which is still 1.5. So it may be a bit before I have time to wait for another build (takes a while to build on Pi) since packages aren't kept up to date for that distribution.

As far as the database host reservations, the documentation for Stork says that it requires the premium hooks plug-in, which last I checked was very expensive for an individual. So I won't be able to afford that. For now, I've just been using custom scripts I wrote a while ago to manage the database host reservations.