Microphone is not working in background (IOS)

## System info

Issue occurs on: iOS (14+)
Plugin version: 0.4.0
Flutter doctor output:

```
here is ok
```

## Steps to Reproduce

1. Join any webRTC meeting via webview (ex: https://whereby.com/)
2. Tap on Home button on your IOS device
3. Now you are able to listen only (microphone is not work in background). If you reproduce this actions with Safari, you get green call overlay on top (and audio and micro would continue work is background)

Start by reproducing the issue on iOS 14+ with plugin version 0.4.0, following the listed WebView meeting steps, and compare the behavior with Safari. The work is done when microphone audio continues after pressing the Home button, alongside the existing listening behavior and green call overlay expectation.

Written by the indexing model from the issue text.