add extra data to certificate endpoint

[gumaerc]

What are the relevant tickets?

Related to https://github.com/mitodl/hq/issues/8009

Description (What does it do?)

This PR replaces the integer ID's on the course_certificates and program_certificates endpoints for course_run and program respectively with the serialized representation of the object they represent. For course_run, CourseRunWithCourseSerializer was used and for program I used ProgramSerializer.

How can this be tested?

• Spin up MITx Online on this branch
• Make sure you have sufficient data to test certificates:
  • Some test courses (Django admin)
  • Some test programs (Django admin)
  • A B2B organization with associated programs (Using B2B management commands, see docs for more detail)
  • Your user should be enrolled in at least one of these courses and have a grade (Enrollments done in the dashboard UI, grades in Django admin)
  • Course run and program certificates created for your user (Django admin and Wagtail)
• Once you have created the course run and program certificates, use their UUID (from Django admin) to hit the certificates URL and ensure that the serialized course run / program are included in the response:
  • /api/v2/course_certificates/uuid-goes-here
  • /api/v2/program_certificates/uuid-goes-here

[jonkafton]

Efficient to have all the data needed to render the certificates on a single endpoint. I've integrated into mitodl/mit-learn#2429 and works great 👍