Do not crash if there are invalid model configs in the DB

[RyanJDick]

Summary

This PR changes the handling of invalid model configs in the DB to log a warning rather than crashing the app.

This change is being made in preparation for some upcoming new model additions. Previously, if a user rolled back from an app version that added a new model type, the app would not launch until the DB was fixed. This PR changes this behaviour to allow rollbacks of this type (with warnings).

Keep in mind that this change is only helpful to users rolling back to a version that has this fix. I.e. it offers no help in the first version that includes it.

QA Instructions

1. Run the Spandrel model branch, which adds a new model type Add support for Spandrel Image-to-Image models (e.g. ESRGAN, Real-ESRGAN, Swin-IR, DAT, etc.) #6556.
2. Add a spandrel model via the model manager.
3. Rollback to main. The app will crash on launch due to the invalid spandrel model config.
4. Checkout this branch. The app should now run with warnings about the invalid model config.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)