Solutions: WP CLI commands and premium plugin utlities

[arunshenoy99]

Story: https://jira.newfold.com/browse/PRESS0-1715

Proposed Changes

1. Three new custom WP-CLI commands:
   • wp installer auto_upgrade_extended_yith_plugins for automatically upgrading extended YITH plugins to their premium versions.
   • wp installer upgrade_extended_yith_plugin <extended_yith_plugin_slug> for manually upgrading a single YITH plugin to it's premium version.
   • wp installer install_premium_plugin <premium_slug> [--activate] for manually installing and/or activating a premium plugin.
2. All these commands are linked to independently usable functions, such as in cases like https://jira.newfold.com/browse/PRESS0-1714.

For now, I have added nfd_slug_yith_paypal_payments_for_woocommerce as the premium plugin slug. We will need to replace this extended-to-premium map with the correct premium entitlement slugs later on.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Video

Checklist

• I have read the CONTRIBUTING doc
• I have viewed my change in a web-browser
• Linting and tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

Lint is failing because I have not tagged a release on wp-module-pls.

[wpscholar]

@arunshenoy99 I think this looks fine for now. I assume we need to update the appropriate slugs before this is merged?

Also, please take a look at my comment here and make sure the PLS module is set up to handle this: https://jira.newfold.com/browse/PRESS0-1714?focusedId=14843090&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14843090