Consider and support "unavailable" power/socket entities

[amitkeret]

I've been using this automation for some time and it's great.

The problem I'm having comes from the fact the state machine does not support a case when the power consumption (or socket) entities become unavailable. In that situation, I think the state machine should switch to unavailable as well.
I have some cards which display entity values, and also monitor and alert if they become unavailable. That doesn't work for the state machine.

See below:

The can icon (for an ultrasonic sensor entity) has an alert since it's unavailable.
The dryer comes up as "off" because the state_machine is idle, even though the underlying power entity is unavailable.