Add source status API and enhance dashboard with data source checks

- Introduced a new API endpoint `/api/source-status/` to return the status of Prometheus and OpenStack data sources.
- Implemented lightweight health check functions for both Prometheus and OpenStack.
- Updated the dashboard template to display the status of data sources dynamically.
- Added tests for the new API endpoint to ensure correct functionality and response handling.
- Configured a cache timeout for source status checks to improve performance.

dashboard/urls.py

@@ -5,4 +5,5 @@ urlpatterns = [
     path('', views.index, name='index'),
     path('api/stats/', views.api_stats),
     path('api/audits/', views.api_audits),
+    path('api/source-status/', views.api_source_status),
 ]