added e2e test for feedback labels

core/signals.py

core/tests/test_subscription_assignment_service.py

...tend/src/components/feedback_labels/FeedbackLabelForm.vue

...d/src/components/feedback_labels/FeedbackLabelUpdater.vue

...end/src/components/feedback_labels/FeedbackLabelsList.vue

frontend/src/components/feedback_labels/LabelSelector.vue

.../src/components/submission_notes/SubmissionCorrection.vue

...tend/src/components/submission_notes/base/CommentForm.vue

...mission_notes/toolbars/ToggleFeedbackVisibilityButton.vue

functional_tests/test_export_modal.py

functional_tests/test_feedback_creation.py

functional_tests/test_feedback_label_system.py

functional_tests/util.py