chore: Changes for GlitchTip support.

We're changing from Sentry to GlitchTip, which is much less
resource-hungry and doesn't require a huge, expensive VM for
itself. This requires a few tweaks to the session initialisation code,
plus we add an error-generating view for testing.

src/ace4/settings.py

@@ -435,16 +435,17 @@ if sentry_dsn is not None:
     from sentry_sdk.integrations.django import DjangoIntegration
 
     sentry_sdk.init(
-        dsn=os.getenv("SENTRY_DSN"),
+        dsn=sentry_dsn,
         integrations=[
             DjangoIntegration(),
         ],
+        auto_session_tracking=False,
         environment=MODE,
 
         # Set traces_sample_rate to 1.0 to capture 100%
         # of transactions for performance monitoring.
         # We recommend adjusting this value in production.
-        traces_sample_rate=1.0,
+        traces_sample_rate=os.getenv("TRACES_SAMPLE_RATE", "1.0"),
 
         # If you wish to associate users to errors (assuming you are using
         # django.contrib.auth) you may enable sending PII data.

src/ace4/urls.py

@@ -41,7 +41,12 @@ class UsernameConverter(StringConverter):
 register_converter(UsernameConverter, "username")
 
 
+def trigger_error(request):
+    division_by_zero = 1 / 0
+
+
 urlpatterns = [
+    path('glitchtip-debug-xyzzy/', trigger_error),
     path('accounts/register/',
          RegistrationView.as_view(form_class=RegistrationForm),
          name='django_registration_register'),