fix: course outline now working for MFE

 This changes fixes the case when:

 1. The course visbility in studio advance settings is set to 'none'.
 2. The `COURSE_ABOUT_VISIBILITY_PERMISSION` is set `see_about_page`.

 The fix is done by assuming that whenever a learner is accsing
 course content and they are **enrolled**, then we use 'load'
 action for them see (course detail/course outline), as oppiste
 to the default which would use `COURSE_ABOUT_VISIBILITY_PERMISSION`
 no matter if learner enrolled or not enrolled.

 Note this change dosn't affect the log `course-id/about` page
 at all, since that view doesn't use this view.

lms/djangoapps/course_api/api.py

@@ -75,8 +75,12 @@ def course_detail(request, username, course_key):
     user = get_effective_user(request.user, username)
     overview = get_course_overview_with_access(
         user,
-        get_permission_for_course_about(),
-        course_key,
+        action=(
+            "load"
+            if CourseEnrollment.is_enrolled(request.user, course_key)
+            else get_permission_for_course_about()
+        ),
+        course_key=course_key,
     )
     overview.effective_user = user
     return overview