Fix media keys support by the Flatpak version

[Anderhar]

Recently, I discovered that my Tor Browser, unlike other applications, does not interact with the multimedia keyboard keys. After a bit of research, I realized that it just didn't have access to the required session bus interface, which is easily fixed by adding its name with flatpak override --own-name=org.mpris.MediaPlayer2.firefox.* com.github.micahflee.torbrowser-launcher (but I simply done the same thing via Flatseal GUI). Suggest to implement this in the default configuration, following the Brave Browser as an example.