Health Check

[pa-wills]

I want to build a system that will check everything periodically, so that I don't have to be so reactive, and so that the loop is closed operationally.

Here are a few thoughts on requirements and structure:

• I want to detect for obviously bad situations, like Entities being Unavailable as occasionally happens with Kasa, etc.
• I want to build the Tests into a library, so that they can then be invoked in response to a variety of scenarios. Some scenarios that I have in mind: Daily Health Check (performed early in the morning), Checks on boot, perhaps some checks that I will run more frequently.
• Notification of results - I think the health check should be mailed, daily. I think also - I should have a Sensor that contains the results of the most recent checks, so that that's displayed in Lovelace.
• This is ideal for AppDaemon.

[pa-wills]

Implemented, with the most recent merge to master.