Save/Load settings

### Problem

Currently there is no in-place upgrade system.
It would be nifty to speed up the process of reinstalling by having a way to save current settings, and later load everything from a Json (in Onboarding for example)

### Proposal

Have eOS expose in About:Plug a Save Settings button

Save: Write to a JSON file some current settings, such as:
-A list of currently Installed flatpaks
-Accent color
-Current accessibility thingamabobs
It does not need to go into details to select what to restore. Just dump it all.

Load: Onboard could integrate later on a button to pull from this save and do all the onboarding

### Prior Art (Optional)

_No response_