Create UI for CSV team management (#22310)

Adds "Manage" sub-tab to course "Teams" tab
with UI for downloading and uploading team
membership CSVs. The upload and download function-
ality are currently not implemented.

The new tab only appears when the user is course staff
and the course has at least one instructor-managed
team-set, which is not the case for any existing
courses, so not current course staff will see this
change.

This ticket will be followed-up upon in MST-44 and
MST-49.

MST-41