Add template information for when grader feedback has been received

This can be used e.g. to show feedback messages from the grading
services that don't want to be permanently shown in the student
feedback, like "Feedback received" in mooc-jutut.

Author: murhum1

exercise/templates/exercise/exercise_plain.html

@@ -203,6 +203,9 @@
 					{% if disable_submit %}
 						data-aplus-disable-submit="true"
 					{% endif %}
+					{% if grader_feedback_just_received %}
+						data-aplus-grader-feedback-just-received="true"
+					{% endif %}
 				>
 					{% include "_messages.html" %}
 					{% include "exercise/_submit_progress.html" %}

exercise/views.py

@@ -248,7 +248,11 @@ def post(self, request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
                 return self.redirect(request.GET["__r"], backup=self.exercise);
 
         return self.render_to_response(self.get_context_data(
-            page=page, students=students, submission=new_submission))
+            page=page,
+            students=students,
+            submission=new_submission,
+            grader_feedback_just_received=True,
+        ))
 
     def submission_check(self, request=None):
         if self.exercise.grading_mode == BaseExercise.GRADING_MODE.LAST: