Add restore state to trigger based template image

originally posted as issue in the github on 2023.7.1, now writing up as FR:

The problem

when using below trigger to create the template image, the dashboard shows a broken placeholder when HA starts, or template integration is reloaded

(we can add some extra triggers for those events, but that updates the template entity, and makes the picture-entity card show a dat of the last trigger, and not the date/time of the last snapshot creation)

related to Template - Home Assistant and of course the trigger based templates section in Template - Home Assistant

Example YAML snippet

template:

  - trigger:

      - platform: state
        entity_id:
          - binary_sensor.oprit_vehicle_detected
          - binary_sensor.oprit_person_detected
        to: 'on'

    image:

      - unique_id: last_snapshot_oprit_camera
        name: Last snapshot oprit camera
        url:

Additional information