feat: force all enrollments

[asadali145]

What are the relevant tickets?

Fixes https://github.com/mitodl/hq/issues/1773

Description (What does it do?)

We are going to mark courses as invite-only in edX to stop direct enrollments in edX. It will require us to force the course enrollments to bypass invitation checks. This PR forces all the course enrollments.

Screenshots (if appropriate):

• Desktop screenshots
• Mobile width screenshots

How can this be tested?

• Make sure that the MITxOnline / edX integration is working
• Enable COURSES_INVITE_ONLY in edX.
• Check out this branch in MITxOnline.
• Verify Audit / Verified Enrollment/Unenrollment, Also, test 100% discount enrollments.
• Verify the following management commands:
  • defer_enrollment
  • transfer_enrollment
  • unenroll_enrollment
  • refund_fulfilled_order
  • retry_edx_enrollment
  • create_enrollment
  • create_verified_enrollment

Additional Context

[arslanashraf7]

On the testing part:

1. I could only test enrollments
2. I couldn't test unenrollment because It's not working. And the reason for that is that we are using user based client instead of service api client while deactivating the enrollments. Take a look at https://github.com/mitodl/mitxonline/blob/main/openedx/api.py#L747 line. Now that we are moving to invitation only courses we would a change in this as well because it eventually calls the enrollment API of edX with is_active=False and the enrollment API doesn't allow this after being Invitation only.
3. Because of unenrollment, I couldn't test defer_enrollment , unenroll_enrollment, unenroll_enrollment etc.

I've created some related issues #1797 and #1798

[asadali145]

As per our discussion, unenrollment looks fine now. Maybe it was some issue with the API keys. Could you please test this PR again?

[arslanashraf7]

I was facing issues with unenrollment but after adding the right value for EDX_API_KEY I was able to test all the cases mentioned in the PR description. So this looks good. 👍

[pdpinch]

This seems ok to merge to me.

When we change the setting in open edX to invite only, we'll need to test carefully & also monitor the logs for any errors.