Recurse into the program if the program doesn't have a verified mode when generating certificates

[jkachel]

What are the relevant tickets?

Closes mitodl/hq#12823

Description (What does it do?)

When determining if the user is eligible for a certificate for a program, recurse into sub-programs if the sub-program only offers audit-mode enrollments.

This also updates the ProgramFactory to generate course modes and updates the affected tests. Also adds a Stripe key to the ecommerce defaults factory - I was getting test errors for that.

How can this be tested?

Automated tests should pass. Note that several tests have changed to accommodate the ProgramFactory changes.

Create a program that only offers audit-mode enrollments. Then, create another program that supports verified-mode enrollments (including a certificate page) and add the first program as a requirement. Create course runs as necessary for these programs as well (you should probably have at least one course in the audit-only program).

Enroll a user in the verified-track program as a verified-track user, in the audit-only program as audit, and the other courses in the appropriate mode (best between verified and audit). Create grades for courses such that the user has a passing grade in everything.

Generate certificates for any course that you've enrolled your user in that has a verified mode. Do this manually (using the Django Admin) because the tasks/commands for this will try to pull grade info from edX. Don't generate a certificate for your verified-mode program yet.

Finally, run _has_earned_program_certificate from courses/api.py in a Django shell with the user and verified-mode program. It should indicate that the user has earned the program certificate. Running the program certificate generation task/etc. should generate a certificate as well.

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