[Feature Request] Allow for per-user Booklore API settings

[FilBr]

Currently, admin users can edit all settings, but Booklore API settings seem to be global (i.e., only one Booklore API configuration is allowed, and changing it for a user changes it for all).

I would love to be able to allow different users to upload to Booklore via APIs by using different credentials, and potentially even to different booklore instances.

[Silenc3IsGold3n]

Even though booklore has been shutdown I'd like to see this continued, as Grimmory ( https://github.com/grimmory-tools/grimmory) has taken up the mantle.