feat: add Course Membership API

The get_course_members API returns a dict of users associated with a course.
This is a potentially expensive operation on a large course, so there is a
control in place to limit its cost.  If a course has more than
settings.COURSE_MEMBER_API_ENROLLMENT_LIMIT enrollments, then the function
raises an OverEnrollmentLimitException.

This API was added to help implement the LTI 1.3 Names and Roles Provisioning
service.

Jira references: [BD-24] [BB-2726] [TNL-7330] 
Pull request: #25843
Co-authored-by: Giovanni Cimolin da Silva <giovannicimolin@gmail.com>

common/djangoapps/student/models.py

@@ -2239,6 +2239,20 @@ class CourseEnrollment(models.Model):
         """
         cache[(user_id, course_key)] = enrollment_state
 
+    @classmethod
+    def get_active_enrollments_in_course(cls, course_key):
+        """
+        Retrieves active CourseEnrollments for a given course and
+        prefetches user information.
+        """
+        return cls.objects.filter(
+            course_id=course_key,
+            is_active=True,
+        ).select_related(
+            'user',
+            'user__profile',
+        )
+
 
 @python_2_unicode_compatible
 class FBEEnrollmentExclusion(models.Model):
@@ -2448,6 +2462,18 @@ class CourseAccessRole(models.Model):
         """
         return (self.role, self.org, self.course_id, self.user_id)
 
+    @classmethod
+    def access_roles_in_course(cls, course_key):
+        """
+        Returns all CourseAccessRole for a given course and prefetches user information.
+        """
+        return cls.objects.filter(
+            course_id=course_key,
+        ).select_related(
+            'user',
+            'user__profile'
+        )
+
     def __eq__(self, other):
         """
         Overriding eq b/c the django impl relies on the primary key which requires fetch. sometimes we