[FEATURE] Support non-standard Steam installations

[orowith2os]

Is your feature request related to a problem? Please describe.
ProtonPlus doesn't work when Steam is installed by way of Distrobox, with a custom home folder set.

Describe the solution you'd like
ProtonPlus should allow setting where Steam is installed (e.g. instead of $HOME/.steam, it should allow $HOME/Subfolder/.steam).

Describe alternatives you've considered
I could install ProtonPlus inside of the container, but I would like to use the Flatpak so it stays in sync with my system and comes directly from here.

[Vysp3r]

That is indeed something that would need to be done.
I will add that to my list.
Thank you for your input!