fix: use single constant for course mode priority; only fetch catalog list with resolved course run

[adamstankiewicz]

Description

1. During stage QA, it was observed that a course run with only an honor seat was not enrollable via the LMS bulk enrollment API when realizing default enterprise enrollment intentions. It was determined that this was due to relying on a constant BEST_MODE_ORDER that didn't include audit/honor seat modes; as such, when trying to enroll in this honor-only course run, it was falling back to attempt to enroll in a non-existent audit seat, resulting in a 409 on the LMS bulk enrollment API. This PR removes BEST_MODE_ORDER to singularly rely on the existing COURSE_MODE_SORT_ORDER instead, which includes honor.
2. When calling the /enterprise/api/v1/default-enterprise-enrollment-intentions/learner-status/ LMS API locally with a default enrollment intention configured for course with a non-existent advertised course run, the DefaultEnterpriseEnrollmentIntention model continues to attempt to call contains_content_items to retrieve a list of applicable catalog UUIDs associated with a resolved course run. However, if a course run cannot be resolved, we shouldn't be making the call to enterprise-catalog, and simply fallback to an empty list in the model's applicable_enterprise_catalog_uuids property.

Merge checklist:

• Any new requirements are in the right place (do not manually modify the requirements/*.txt files)
  • base.in if needed in production but edx-platform doesn't install it
  • test-master.in if edx-platform pins it, with a matching version
  • make upgrade && make requirements have been run to regenerate requirements
• make static has been run to update webpack bundling if any static content was updated
• ./manage.py makemigrations has been run
  • Checkout the Database Migration Confluence page for helpful tips on creating migrations.
  • Note: This must be run if you modified any models.
    • It may or may not make a migration depending on exactly what you modified, but it should still be run.
  • This should be run from either a venv with all the lms/edx-enterprise requirements installed or if you checked out edx-enterprise into the src directory used by lms, you can run this command through an lms shell.
    • It would be ./manage.py lms makemigrations in the shell.
• Version bumped
• Changelog record added
• Translations updated (see docs/internationalization.rst but also this isn't blocking for merge atm)

Post merge:

• Tag pushed and a new version released
  • Note: Assets will be added automatically. You just need to provide a tag (should match your version number) and title and description.
• After versioned build finishes in GitHub Actions, verify version has been pushed to PyPI
  • Each step in the release build has a condition flag that checks if the rest of the steps are done and if so will deploy to PyPi.
    (so basically once your build finishes, after maybe a minute you should see the new version in PyPi automatically (on refresh))
• PR created in edx-platform to upgrade dependencies (including edx-enterprise)
  • Trigger the 'Upgrade one Python dependency' action against master in edx-platform with new version number to generate version bump PR
  • This must be done after the version is visible in PyPi as make upgrade in edx-platform will look for the latest version in PyPi.
  • Note: the edx-enterprise constraint in edx-platform must also be bumped to the latest version in PyPi.

[adamstankiewicz]

[inform/context] This removed constant has the same ordering as COURSE_MODE_SORT_ORDER, save for CourseModes.UNPAID_EXECUTIVE_EDUCATION. However, I believe this is OK as course runs with a seat mode of CourseModes.UNPAID_EXECUTIVE_EDUCATION do not have any seats with mode of CourseModes.AUDIT or CourseModes.HONOR.