Add a check to ensure we have a valid PHP version before loading plugin functionality and output an admin notice if needed

[kmgalanakis]

Description of the Change

In this PR, I'm adding a check for the minimum required PHP version before attempting to load the plugin files. If the condition is not met an admin notice is displayed and the plugin files are not loaded.

Closes #220

How to test the Change

• To see the admin notice and have the plugin functionality not loaded, try to load the plugin on a site with PHP version lower that 7.4.

Changelog Entry

Added - Check for minimum required PHP version before loading the plugin

Credits

Props @kmgalanakis

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.
  c

[faisal-alvi]

@kmgalanakis Thank you for the PR.

Status: 👍🏻

I've tested and observed that when the plugin is inactive, and the site is utilizing a PHP version lower than the requirement, WordPress displays a message on the plugin list page. This prevents users from activating the plugin.

However, in the scenario where the plugin is already activated, the expected error notice is displayed, as shown below.