[Feature] Sync in current Firefox container

Motivation
Syncing to Google / DropBox / any online service never worked for me and never will because I use containers for sessions separation and it's impossible (I think) to tell Violentmonkey which container to use when making a backup. When I hit "authorize" button it always opens a sign-in page in the default container where I'm never logged in (and can't be for security reasons).

Proposed Solution
It'd be awesome if Violentmonkey just synced scripts and settings to Firefox Sync like some other Firefox plugins do. Firefox Sync doesn't share its session with websites so it's cross-site attack immune by definition and doesn't care for containers. Implementation might not be trivial because it seems not every aspect of it is properly documented, as stated in Mozilla wiki:

Build a Sync engine (if you need to sync more than just preferences). If you need this, please drop by the #sync channel in IRC so you can chat with a Sync developer (there are some important details not currently captured formally in any docs).

Use Cases
Because of the above, as a user who was making ZIP backups manually (actually by a cron-triggered JS script) and lost them today due to carelessly executed bleaching/privacy software (same would happen if a local ZIP file became unreadable for whatever reason), I'd like Violentmonkey to keep a backup in the cloud (preferably by default) making such cases less of a disaster.

Start by tracing the existing authorize flow mentioned in the issue and read Mozilla's Add-on Sync documentation linked there. Determine the scope of scripts and settings that must sync through Firefox Sync, then define how successful backup, restoration, and Firefox container behavior would be verified.