fix: add middleware for datadog (#331)

edx_exams/settings/base.py

@@ -60,6 +60,7 @@ def root(*path_fragments):
     'edx_django_utils.cache.middleware.RequestCacheMiddleware',
     # Enables monitoring utility for writing custom metrics.
     'edx_django_utils.monitoring.middleware.MonitoringCustomMetricsMiddleware',
+    'edx_django_utils.monitoring.DeploymentMonitoringMiddleware',
     'corsheaders.middleware.CorsMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',
     'django.middleware.locale.LocaleMiddleware',