Prompt for additional codec installation

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

## Feature
**Is your feature request related to a problem? Please describe.**
Most of my music are [.m4a](https://medium.com/@ontiva/m4a-vs-mp3-the-differences-pros-and-cons-and-how-to-convert-from-m4a-to-mp4-960631368609) files, but unfortunately I can't play this common file format using this application on a newly set up elementary OS 6 (early access) system. Everything works after installing the `gstreamer1.0-libav` package.

**Describe the solution you'd like**
Add `gstreamer1.0-libav` as a dependency - people expect a music player to be able to play most of their music, so I think this should definitively be a dependency, or at least pre-installed on elementary OS.

**Existing work**
See gstreamer1.0-libav

**Describe alternatives you've considered**
Use another music player, or install gstreamer1.0-libav manually