Option to change proton's wine-prefix on per-user basis

[BillGHero]

Feature Request

I confirm:

• [confirmed ] that I haven't found another request for this feature.
• [confirmed ] that I have checked whether there are updates for my system available that
  contain this feature already.

Description: Option to allow a user logged into a steam client on a PC/machine to have their own wine prefix for each game they play such that the save files from their sessions do not interfere with save files from other users on that machine. The only reasonable alternative at this time is to install multiple copies of a game and this can result in a massive waste of storage space due to the size of many game's content files. For instance I have tried specifying a different wine prefix using WINEPREFIX but proton/steam ignores the directive and continues to save in the default prefix for Cyberpunk 2077.

Justification [optional] This is something that was not implemented but could be. Add one folder layer to the prefix folders for the game/application. Within that root folder have one prefix for each user that logs into that steam client. This would allow users to have their save games files discrete from each others and not have to duplicate install files, not have to duplicate patching. You could even, reasonably, say that it saves electricity and internet bandwidth - because it would.

Risks [optional]

References [optional]

[kisak-valve]

Hello @BillGHero, this issue is already being tracked at ValveSoftware/steam-for-linux#6958. Closing as a duplicate.