Allow TTS notification to speak as loud as possible using alarm stream, then restore volume

[dshokouhi]

Summary

Sometimes a user may find their device might be speaking too low due to the volume level. Using TTS we are able to detect when a stream is going to start and when it has been completed. We can then change the volume level and set it to the max and restore it once completed. This can be useful for a user who wants an important notification spoken as loud as possible.

Screenshots

N/A

Link to pull request in Documentation repository

Documentation: home-assistant/companion.home-assistant#381

Any other notes

Example:

    - service: notify.mobile_app_<your_device_id_here>
      data:
        title: "The house is on fire and the cat's stuck in the dryer!"
        message: TTS
        data:
          ttl: 0
          priority: high
          channel: alarm_stream_max