Add mount paths to secondary drives

[termdisc]

/run/media/... and /mnt/... are common mount paths for secondary drives where people may install their games. For example, a Steam Deck mounts an SD card at /run/media/deck/<UDID>. Desktop installations may use /mnt for permanently mounted drives as well.

Adding these permissions out the gate would mitigate the initial prompt about not having sufficient permissions to access folders.

[termdisc]

This looks like a broader version of #136

[flathubbot]

Started test build 175090

[flathubbot]

Build 175090 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/158227/com.github.Matoking.protontricks.flatpakref

[Matoking]

As far as I know, Flathub applications should not be given broad permissions by default unless really necessary (there are requirements detailed here). I don't believe adding these broad permissions are justified given that there is already a prompt, even if it's a bit janky. This would ideally be solved with a proper API on the Flatpak side or an XDG Portal, but neither is available at the moment.

For what it's worth, the Steam Flatpak only has access to its own app directory by default with instructions in the wiki for external disks should the user want to add any.

[termdisc]

The linked requirements further links to "Flatpak permissions guide," which also includes a section for external drives. This section includes /mnt, /run/media and one that I neglected to include: /media.

I believe that these are within the scope of these guidelines, especially when you take into account the increase of handheld PCs running SteamOS or SteamOS-like distros.

[flathubbot]

Started test build 175610

[flathubbot]

Build 175610 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/158753/com.github.Matoking.protontricks.flatpakref

[flathubbot]

Started test build 176801

[flathubbot]

Build 176801 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/159955/com.github.Matoking.protontricks.flatpakref