Add Sub Menu observer for Pro Modules

[Soare-Robert-Daniel]

Summary

This a completion of this recommendation https://github.com/Codeinwp/neve-pro-addon/pull/2673#pullrequestreview-1717999564

I added a reusable script that checks the Custom Layout status and adds/removes the Sub Menus based on module status.

This will offer visual feedback to the user regarding the module status.

Will affect visual aspect of the product

YES

Screenshots

2023-11-07_14-21-08.mp4

Test instructions

⚠️ You will to test with Neve Pro, and it must be tested with this PR https://github.com/Codeinwp/neve-pro-addon/pull/2701 . If the PR has been merged, use the release build.

• When you toggle Custom Layouts, you should see how the Sub Menu is added or removed.

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/neve-pro-addon/issues/2671

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🎉 This PR is included in version 3.7.4 🎉

The release is available on GitHub release

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