Show upsell popup when editing pro fields

[girishpanchal30]

Summary

Added upsell popup and show it when editing the lock field if a license is expired or not available.

Will affect visual aspect of the product

YES

Screenshots

https://tinyurl.com/2bmmgwuf

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/381

[pirate-bot]

Plugin build for ffbc0bc is ready 🛎️!

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[rodica-andronache]

@girishpanchal30 I've tested with no license entered at all.
In this case, I got these warnings

Also, after clicking on the Renew License button, I am redirected to this, not sure if correct

[girishpanchal30]

@rodica-andronache I fixed the warnings and the Renew License URL is working for me, please check with the latest build zip.

[AndreeaCristinaRadacina]

@girishpanchal30 I tested it now, and it works as expected!

One question: should we add an overlay to make the rest of the screen not accessible anymore?
Right now, while I have the alert on the screen, I can still perform other actions, like enabling/disabling fields:

I can even switch to the style tab and write some code.

[girishpanchal30]

@AndreeaCristinaRadacina Added background overlay, please check with the latest commit.

[AndreeaCristinaRadacina]

@girishpanchal30, perfect! It works as expected!