[Previews] Audio preview

As a user, i want the possibility to play an audio file on the ownCloud iOS App

AC:

• The file should be streamed (not downloaded).
• The audio should works also in background.
• The audio should be controlled also by the system controls (MPRemoteCommandCenter ):
  • Play/Pause
  • [ ] Previous button
  • [ ] Following button
  • [ ] Title, album, artist metadata
  • [ ] Cover
• [ ] The player should show the metadata information of the audio file if it exist (if not show a default image and the file name without the extension instead the title of the audio file).
  • Cover
  • [ ] Title
  • [ ] Album - Artist
• The player should have in memory all the list of audio file of the current folder in order to player the following and back one.
• [ ] If there are not more following or back songs the "Previous" or "Following" buttons should appear disabled.
• [ ] The first time than the player open a new audio files (metadata not read yet) the player should show the view as an audio file without metadata and then update it with the image, title, album and artist

Mockups:

Figma design:
https://www.figma.com/file/Ui4YzD3oQcxJSbzBEr80O9eU/Working-Draft-UI?node-id=1657%3A2327

Start by reviewing the acceptance criteria and the linked mockups and Figma design. Define the iOS audio-preview entry points before implementation; done means the listed streaming, background playback, system controls, metadata, cover, playlist navigation, and disabled-button behaviors are covered.