Refactor test utilities and enhance ASGI settings

- Cleaned up and standardized assertions in ApiTestMixin for API response validation.
- Updated ASGI settings to use os.environ for setting the DJANGO_SETTINGS_MODULE.
- Removed unused imports and improved formatting in settings.py.
- Refactored URL patterns in urls.py for better readability and organization.
- Enhanced view functions in views.py for consistency and clarity.
- Added .flake8 configuration for linting and style enforcement.
- Introduced type stubs for django-environ to improve type checking with Pylance.

email_service/migrations/0001_initial.py

@@ -43,7 +43,8 @@ class Migration(migrations.Migration):
                 (
                     "site",
                     models.ForeignKey(
-                        on_delete=django.db.models.deletion.CASCADE, to="sites.site"
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to="sites.site",
                     ),
                 ),
             ],
@@ -55,7 +56,10 @@ class Migration(migrations.Migration):
         migrations.CreateModel(
             name="EmailConfigurationEvent",
             fields=[
-                ("pgh_id", models.AutoField(primary_key=True, serialize=False)),
+                (
+                    "pgh_id",
+                    models.AutoField(primary_key=True, serialize=False),
+                ),
                 ("pgh_created_at", models.DateTimeField(auto_now_add=True)),
                 ("pgh_label", models.TextField(help_text="The event label.")),
                 ("id", models.BigIntegerField()),