CONTENT_GROUPS_FOR_TEAMS breaks across re-runs and import/export

The Problem

The id that TeamPartitionScheme passes into the Group is the primary key of the corresponding CourseTeam object: https://github.com/openedx/edx-platform/blob/master/lms/djangoapps/teams/team_partition_scheme.py#L102

These primary keys will be written into published learning content via the group_access XBlock attribute from InheritanceMixin, and the keys will be written into XML when exporting. Primary keys are not appropriate for this, because they will have different meanings across different course runs and across different instances.

Steps to reproduce

(This is just based on reading the code. I haven't tried these steps yet)

• Enable CONTENT_GROUPS_FOR_TEAMS waffle
• Create a course and configure a team-set
• Publish it
• In LMS, create a couple teams
• In Studio, restrict some content to those teams
• Re-run the course
• In the re-run, create the same two teams
• Expected: In the re-ran course, team access restrictions will still be in place.
• Actual: In the re-ran course, team access restrictions will point to CourseTeams object from the original run, and thus won't work and/or will raise an error.

Start at lms/djangoapps/teams/team_partition_scheme.py around line 102 and trace how InheritanceMixin stores group_access through course export/import and re-runs. Reproduce the CONTENT_GROUPS_FOR_TEAMS scenario if possible; done means restrictions in a re-run resolve to that run's teams rather than the original CourseTeam records.