Integrate watchdog hardware support

[mbtown01]

Good write-up of how to do this mostly with systemd and some python below:

https://www.medo64.com/2019/01/systemd-watchdog-for-any-service/

[mbtown01]

This feature is potentially working too well, restarting the thermostat a few times when it tries to start up. Need to double-check this. One thought I had was to make the 'petting of the dog' a service and then have some kind of web-based control indicating whether we are actively managing the watchdog or not. Currently, if watchdog isn't setup we don't even try to pet it!