Ensure the ClassifAI Registration settings can be saved properly

[dkotter]

Description of the Change

In setting up a new environment, I was getting an error when trying to save the ClassifAI Registration settings. In looking at the code, the problem is we grab the existing settings and merge those in to the saved settings. But if no settings exist yet, we end up trying to merge a string into an array, which throws a PHP error.

This PR fixes that by ensuring the default for our settings is an array.

How to test the Change

1. Set up a new environment or in an existing environment, delete the classifai_settings option
2. If not on this branch, try saving the ClassifAI Registration settings and see you'll get an error
3. Check out this branch and try again, settings should now save

Changelog Entry

Fixed - Ensure the ClassifAI Registration settings save correctly

Credits

Props @dkotter

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[iamdharmesh]

LGTM 🚀