Add OpenAI Embeddings in the Classic Editor Support

[phpbits]

Description of the Change

This PR adds the ClassifAI metabox for the classic editor for OpenAI Embeddings support.

Closes #496

How to test the Change

• Set up an integration with OpenAI in Language Processing > OpenAI Embeddings
• Ensure the Classify content option is turned on and at least one Post type that has the block editor disabled.
• In whatever taxonomy you've selected, ensure you have one or more terms saved
• Create a new piece of content and publish that content (or match whatever post status option you selected)
• Ensure one or more terms gets auto-assigned

Credits

Props @phpbits

Checklist:

• I agree to follow this project's Code of Conduct.

[phpbits]

@jeffpaul @dkotter This is now ready for code review and QA. Thanks!

[dkotter]

Would also be great to add a Cypress test here to ensure this metabox shows properly in the Classic Editor. See https://github.com/10up/classifai/pull/518/files#diff-c4172826b0f360a287099211a31d6a1b8bee386d8dc8b6b5059730bfa77d4b30R84 for an example of how to do this

[phpbits]

Would also be great to add a Cypress test here to ensure this metabox shows properly in the Classic Editor. See https://github.com/10up/classifai/pull/518/files#diff-c4172826b0f360a287099211a31d6a1b8bee386d8dc8b6b5059730bfa77d4b30R84 for an example of how to do this

@dkotter I've added one but it seems to be failing. Would you mind checking it out? Thanks!