feat: add first batch of Open edX Filters

* Add PreEnrollmentFilter
* Add PreRegisterFilter
* Add PreLoginFilter

For more info: openedx/edx-platform#29449

Some events that were already on the platform were also added:
* Add COURSE_ENROLLMENT_CHANGED: sent after the enrollment update
* Add COURSE_ENROLLMENT_CREATED event after the user's enrollment creation
* Add COURSE_UNENROLLMENT_COMPLETED: sent after the user's unenrollment

For more info:
openedx/edx-platform#28266
openedx/edx-platform#28640

Author: mariajgrimaldi

common/djangoapps/student/models.py

@@ -66,6 +66,7 @@
     COURSE_ENROLLMENT_CREATED,
     COURSE_UNENROLLMENT_COMPLETED,
 )
+
 from openedx_filters.learning.filters import CourseEnrollmentStarted, CourseUnenrollmentStarted
 import openedx.core.djangoapps.django_comment_common.comment_client as cc
 from common.djangoapps.course_modes.models import CourseMode, get_cosmetic_verified_display_price

common/djangoapps/student/tests/test_filters.py

@@ -2,15 +2,19 @@
 Test that various filters are fired for models/views in the student app.
 """
 from django.http import HttpResponse
-from django.test import override_settings
 from django.urls import reverse
-from openedx_filters import PipelineStep
 from openedx_filters.learning.filters import DashboardRenderStarted, CourseEnrollmentStarted, CourseUnenrollmentStarted
 from rest_framework import status
+
+
+from common.djangoapps.student.models import UnenrollmentNotAllowed
+
+from django.test import override_settings
 from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase
 from xmodule.modulestore.tests.factories import CourseFactory
-
-from common.djangoapps.student.models import CourseEnrollment, EnrollmentNotAllowed, UnenrollmentNotAllowed
+from openedx_filters.learning.filters import CourseEnrollmentStarted
+from openedx_filters import PipelineStep
+from common.djangoapps.student.models import CourseEnrollment, EnrollmentNotAllowed
 from common.djangoapps.student.tests.factories import UserFactory, UserProfileFactory
 from openedx.core.djangolib.testing.utils import skip_unless_lms
 
@@ -109,7 +113,6 @@ def run_filter(self, context, template_name):  # pylint: disable=arguments-diffe
             response=response,
         )
 
-
 @skip_unless_lms
 class EnrollmentFiltersTest(ModuleStoreTestCase):
     """