feat: reimagine certificate display settings
The course settings `certificate_available_date` (CAD) and
`certificates_display_behavior` (CDB) were previously
acting indedependantly of one another. They now work in
tandem. This change:
- limits CDB to a dropdown
- removes "early_with_info" and adds "end_with_date"
- only takes CAD into account if "end_with_date" is selected
- Moves CDB to the main course schedule settings page
- updates CourseOverview model and CourseDetails objects to
validate these fields and choose sane defaults if they aren't
expected values
This work was previously done in bd9e7dd (complete with bugs), so this
version is toggleable via the ENABLE_V2_CERT_DISPLAY_SETTINGS setting
This moves all course runs that use certificates over to V2 of course certificates, and disables the option for a course run to use V1 of course certificates.
MICROBA-1082
[MICROBA-1109]
* Remove the requirement for the `auto_certificate_generation` waffle switch to be enabled in order for a learner to be eligible for a certificate. This switch should control _when_ a certificate is generated, not _if_ a certificate will be generated for a learner.
* Move the `auto_certificate_generation_enabled` check to happen before we try to generate v2 certificates in signals.py
* Update unit tests
* Update documentation
