[ET-2015] Adjusted the logic for calculating fees when using Stripe.

[redscar]

🎫 Ticket

ET-2015

🗒️ Description

In a previous PR (#2403) we removed certain parts of the is_licensed_plugin logic due to its resource-intensive nature, especially noticeable on the checkout page when Stripe is enabled. This PR reintroduces the logic with the idea of caching the revalidation of id_current_license_valid.

Scenario -
When $revalidate is true we need to check the most recent license. This happens here. This method is always called when you checkout for Stripe to see if the fee must be added.

I added in additional caching when $revalidate is true. The cache will only last an hour and will help alleviate multiple calls to is_current_license_valid which is resource intensive.

I originally tackled this using Tribe Cache. However, I found that the value wasn't being kept in the cache and it was blank every page load. Therefore I moved forward using transients instead.

🎥 Artifacts

✔️ Checklist

• Changelog entry in the readme.txt file.
• Code is covered by NEW wpunit or integration tests.
• Code is covered by EXISTING wpunit or integration tests.
• Are all the required tests passing?
• Automated code review comments are addressed.
• Have you added Artifacts?
• Check the base branch for your PR.
• Add your PR to the project board for the release.