Problem/Motivation
It is currently not possible to configure an audio file using FileAudioFormatter to be muted by default.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/audio#Attributes
Solution
This configuration currently exists in FileVideoFormatter and works properly. Since both the audio and video formatters share FileMediaFormatterBase, moving the muted setting to that class provides this option to both formatters without breaking any existing config for videos.