[UX] Add option to backup saves after closing a game

[arielj]

I'm not 100% convinced about this feature as implemented in this PR. I do think that having a way to backup save files before doing some sync is a good idea because I've seen many support tickets of users playing around with cloud saves and ending up losing their saves for different reasons.

This PR adds an option to copy the saves of a game into Heroic's config folder after the game closes if it supports cloud saves and they are enabled.

I think we can only implement this for games with cloud saves since those are the ones we can know the save path from the metadata.

I don't know if the approach here is the best idea so I'm open to any feedback. Other options could be:

• backup BEFORE syncing when launching a game
• backup BEFORE syncing both when launching a game and when running the sync manually (maybe this is safer for what I'm trying to avoid?)
• backup with a button (though users might expect some kind of restore button in that case)

I also don't know how big save files can get (I know GOG added some limits, but I don't know about Epic). Maybe we have to put some limit in the number of backups per game? I'm not sure either

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)