Feature #19822, users can preview audio in a repository.

This MR would allow users to preview audio from within a repository.

This is a follow-up to !17860 (merged) which these changes depend on.

Screenshots

Before	After

Help Wanted

1. Doing a global search through the specs for 'video', I could not find any tests relevant to these changes. I could use feedback on what particular tests would need to be included with these changes.
2. I was unclear of when and where the switcher icon, self.switcher_icon = 'file-audio-o', comes into play (see blob_viewer/audio.rb). I believe file-audio-o would be the appropriate one to use, but I am not certain.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry

• Code review guidelines

• Style guides

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

• Tested in all supported browsers
  - Tested in Chrome and Firefox. These changes make use of the native HTML5 audio element, which is supported by all Gitlab-supported browsers.

#19822 (closed)