fix(memberships): reset end date on subscription

[miguelpeixe]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

An alternative approach for #3768 and #3393.

There's a known bug that Woo Memberships doesn't reset a membership's "end date" if a subscription reactivates it. On a cron routine, the end date value will get picked up and expire the membership.

This approach hooks into a subscription status update to manually reset the end date of a membership attached to it.

How to test the changes in this Pull Request:

Same steps from #3768

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[miguelpeixe]

Superseded by #3768