Assist Notification sound when ready for input.

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

I'm using Hearing aids with tap-control to enable the assist function (Double-Tap my ear/HearingAid). I then give my voice command and then nothing happens.... Sometimes the Double-tap isn't registered, so assist isn't started, while I already start to give commands.

**Describe the solution you'd like**

It would be nice to have a (confgurable) audible notification that lets me know that Assist is ready for a command.

**Describe alternatives you've considered, if any**

**Additional context**

Using a Bluetooth Hearing Aid: `Phonak Audeo I70 Sphere`, that uses the classic bluetoth protocol and acts just like a headphone.

Phone: `Motorola Edge 50 Neo` with `Android 15`

HomeAssistant Companion: `v2025.2.3-full`