ios "InputGain" options

[Volsavr]

Implemented a few options related to microphone

if (_avAudioSession != null) {

       var gainValue = mute? 0.00001 : 1.0;
       var result = await _avAudioSession?.setInputGain(gainValue);

       _logger.log(LogLevel.debug,
           "AudioManager", "New InputGain state: ${gainValue.toString()} ${result?.toString()}");
}