Feature: ability to detect audio input/output changes, especially for BT

[davidzhao]

Is your feature request related to a problem? Please describe. When the user plugs in a BT device, LiveKit switches audio input/output to it automatically. This is correct.

However, the app developer isn't know that the underlying input/output device has changed. This is particularly useful if the application has UI indicating if the current input/output is BT vs mic/speaker

Describe the solution you'd like Being able to automatically detect this via DeviceManager and/or emit events when changes are detected

[davidliu]

Is there an existing standard JavaScript interface for this or should I just expose it separately?