Add device_class to the Alert integration [PAID]

I’m willing to pay $20 for this PR, paid via PayPal or Venmo once PR is submitted (as long as it works correctly).

Currently, the Alert integration requires an entity_id. Instead, I’d like to trigger it with a domain and device_class. For example, trigger an alert if any moisture sensors trip.

An example configuration would be:

alert:
  leak_detected:
    name: Leak Detected! 
    done_message: Water has been cleared
    domain: binary_sensor
    device_class: moisture
    state: "on"
    repeat: 30
    can_acknowledge: true
    notifiers:
      - ryans_phone