MailChimp for WooCommerce Memberships 1.5.0

* Misc - Add compatibility for WooCommerce High Performance Order Storage (HPOS)
* Misc - Require PHP 7.4+

* Fix - Improve Background Job Handler compatibility with newer WooCommerce versions while processing a job queue
* Fix - Replace deprecated `is_ajax()` function calls with `wp_doing_ajax()`
* Misc - Require WooCommerce 3.9.4 or newer

* Misc - Add compatibility for WooCommerce 4.7
* Misc - Require PHP 7.0 or newer