Fix/add compatibility product add on gravity add on

[alexiglesias31]

All Submissions:

• [x] Does your code follow the Extendables standards?
• [x] Have you written new tests for your changes, as applicable?
• [x] Have you successfully run tests with your changes locally?

Changes proposed in this Pull Request:

Fix compatibility issues with Woo Product Add-On and Gravity Forms Add-On

How to test the changes in this Pull Request:

1. Install a built version of this PR.
2. Install and setup Gravity Forms Add-On and Product Add-On.
3. The extra fees added by the Add-On should be added as well using the Express Checkout from the product page.

Changelog entry

Fix - Compatibility with Woo Product Add-On Fix - Compatibility with WooCommerce Gravity Forms Product Add-Ons

[alexiglesias31]

@dpanta94 some extra fixes for the following issues:

• https://app.clickup.com/t/86drg2pgh
• https://app.clickup.com/t/86drgg6zx
• https://app.clickup.com/t/86drgqht4