feat: allow product search on Attach to Product select

[Soare-Robert-Daniel]

Summary

• A new endpoint was created so that the Attach to Product select can now be enhanced with a search to support thousands of products. This replaces the original implementation in which we pull all the products at once.

Will affect visual aspect of the product

NO

Screenshots

Test instructions

• Add lots of products (You can use https://wordpress.org/plugins/woocommerce-product-generator/ )
• Check if the Attach to Product select loads them progressively, and it can search.

Check before Pull Request is ready:

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

Closes https://github.com/Codeinwp/ppom-pro/issues/645

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