PTT button during call or jitsi conferencing

During a call, it would be nice to be able to mute the microphone and hold down the headphone button to unmute the microphone until I let go. In this way I can be doing something with my hands and have my phone in my pocket and simple press the headphone button to talk on a conference call.

No file, test, or entry point is named in the issue. Start by reproducing the behavior in an iOS call or Jitsi conference and locating the call audio controls and headphone-button handling; done means holding the button unmutes the microphone and releasing it mutes again.

Written by the indexing model from the issue text.