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/prometheus_utils/query.py

@@ -2,6 +2,29 @@ import requests
 
 from watcher_visio.settings import PROMETHEUS_URL
 
+# Timeout for lightweight health check (seconds)
+CHECK_TIMEOUT = 5
+
+
+def check_prometheus() -> dict:
+    """
+    Lightweight check that Prometheus is reachable.
+    Returns {"status": "ok"} or {"status": "error", "message": "..."}.
+    """
+    url = f"{PROMETHEUS_URL.rstrip('/')}/api/v1/query"
+    try:
+        response = requests.get(url, params={"query": "1"}, timeout=CHECK_TIMEOUT)
+        response.raise_for_status()
+        data = response.json()
+        if "data" in data and "result" in data["data"]:
+            return {"status": "ok"}
+        return {"status": "error", "message": "Invalid response"}
+    except requests.RequestException as e:
+        return {"status": "error", "message": str(e) or "Connection failed"}
+    except (ValueError, KeyError) as e:
+        return {"status": "error", "message": str(e) or "Invalid response"}
+
+
 def query_prometheus(query: str) -> str | list[str]:
     url = f"{PROMETHEUS_URL}/api/v1/query"
     params = {