Add isSelectableByUser attribute to product templates

[nathanss]

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

How to test the changes in this Pull Request:

Using the WooCommerce Testing Instructions Guide, include your detailed testing instructions:

1. Enable the new product editor at /wp-admin/admin.php?page=wc-settings&tab=advanced&section=features
2. Go to Products > Add
3. Click on 'Change product type'
4. Check the templates that are listed
5. Install and enable the following plugin:
   test-product-template.zip
6. Refresh the product page
7. Check the templates again, you should NOT see a new template on the list, since the one added by the plugin has isSelectableByUser equal to false

Changelog entry

• Automatically create a changelog entry from the details below.

Significance

• Patch
• Minor
• Major

Type

• Fix - Fixes an existing bug
• Add - Adds functionality
• Update - Update existing functionality
• Dev - Development related task
• Tweak - A minor adjustment to the codebase
• Performance - Address performance issues
• Enhancement - Improvement to existing functionality

Message

Comment

[mattsherman]

Tested well and code looks good. Just a minor comment about improving the changelog entry.

[mattsherman]

It would be useful to say why the attribute is being used.

[github-actions]

Hi @mattsherman,

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[mattsherman]

Thanks for updating the changelog entry. Looks good!