* feat: Add EnrollmentsService in XBlockRuntime and block renderer
These changes give ability to use `EnrollmentsService` in XBlocks
Add `get_active_enrollments_by_course_and_user` method to `EnrollmentsService` which can be used to get active enrollment of user for a give course
* The original use of user.has_perm('can_take_proctored_exam') in the get_active_enrollments_for_course method had very poor performance when used for multiple learners. The permission is not designed for use in bulk operations. It was being called for each user in a loop by edx-proctoring, resulting in many queries to the database. This lead to timeouts on the client. This change exposes a new service endpoint that performs this permission checking in the database, resulting in one single query to the necessary LMS SQL tables and many fewer queries to the modulestore.
* bump version of edx-proctoring to 3.7.3
