[FEAT] Add mpv detection for media

[michirakara]

Wanted features:

Detect mpv for media

Motivation:

mpv is a very popular media player as it has 28.3k stars in github, while vlc, which is supported in fastfetch, has 14.1k stars, so it would be nice to detect mpv as a media source.
(I tried to make PR but I couldn't figure out how the DBus library is working. If someone could teach me about it, I would try to implement this.)

[CarterLi]

It's because mpv lacks built-in support of MPRIS standard

You may enable it with some 3rd-party plugins. Try mpv-mpris

[michirakara]

It worked. Thanks!