[Task] - Fix common backup-restore issues instead of dumping data

[michael-genson]

What is the problem this task addresses?

Currently, when restoring a backup, any rows with invalid foreign keys are dropped (see #2986). This is a fair "catch-all" solution, but we can do better for more common issues (such as #3171)

Proposed/Possible Solution(s)?

Scan the database JSON before attempting to import and fix some common issues. Specifically, looking at #3171, I can think of two:

1. If an invalid user_id is found, replace it with a valid one (find any admin user, similar to: feat: Filter Out Shopping Lists That Aren't Yours #3213)
2. If an invalid group_id is found, replace it with a valid one (using an admin user, same as above)

This should fix the most egregious of errors (e.g. deleting recipes that belong to missing users)

[tba-code]

It would be kind of nice if there was a placeholder user and group that could be used for orphaned entries. like a group that you cant be added to, and a user that cant be logged in as that are just for placeholders in these situations.