Is your feature request related to a problem? Please describe.

When I listen to speech(audiobook, podcast, news,etc.) on my home sound system, assist can not distinguish between my voice and surrounding sound, and never stops listening.

Describe the solution you'd like

I would like to mute my home sound system, when assist is listening (like I do with Voice PE).
To do this we need a sensor in the companion-app, that shows, whether assist on the phone is listening.

We could have different state

• CLOSED: Assist is not opened
• SPEAKING: Assist is speaking
• LISTENING: Assist is listening
• IDLE: Assist is opened but not doing anything

This feature request comes from https://community.home-assistant.io/t/sensor-for-assist-listening-on-phone/907054