feat: AA-773: Add in logic to mark special exams as complete

We have had numerous support tickets/bugs related to special exams
not properly displaying completeness (see https://openedx.atlassian.net/browse/AA-773 for
details). Along with a corresponding edx-proctoring PR, this will now
submit completions for all completable children within a special
exam upon the exam being completed for the first time (as dictated by
the logic in the edx-proctoring PR).