Ninja Forms - Stripe Addon 3.2.4

* Update library for PHP 8
* Add metabox to new core submissions page

*Bugs:*

* Resolved an issue that was causing a conflict with our PayPal Express add-on accepting payments on the same form.

*Changes:*

* Added a trial period setting for subscriptions in the Stripe action. This is to resolve Stripe's support deprecation of trial periods defined on plans.

*Bugs:*

* Stripe associated merge tags should now be working properly in actions.
* Product descriptions now properly save on Stripe's end.
* Resolved an issue that was causing live transactions to display as test data in the submission editor.
* Forms should now properly complete after payment on forms that do not have a store submission action.
* Resolved an issue that sometimes caused an Invalid Positive Integar error on form submission.