Add dashboard statistics module and refactor views for metrics handling

- Introduced a new `stats.py` module to encapsulate dashboard statistics building and cache key constants.
- Refactored `views.py` to utilize the new `build_stats` function for constructing metrics context, improving code organization and readability.
- Updated Prometheus query handling to streamline metrics fetching with a new `fetch_dashboard_metrics` function.
- Enhanced test cases to reflect changes in metrics fetching and context building, ensuring accurate functionality.
- Added new HTML templates for displaying detailed resource allocation and flavor statistics on the dashboard.

dashboard/tests/test_views.py

@@ -96,7 +96,7 @@ class CollectContextTest(TestCase):
         return conn
 
     @patch("dashboard.views.get_current_cluster_cpu")
-    @patch("dashboard.views._fetch_prometheus_metrics")
+    @patch("dashboard.views.fetch_dashboard_metrics")
     @patch("dashboard.views.get_audits")
     @patch("dashboard.views.get_flavor_list")
     @patch("dashboard.views.get_connection")
@@ -152,8 +152,6 @@ class CollectContextTest(TestCase):
         self.assertEqual(context["flavors"]["first_common_flavor"]["name"], "m1.small")
         self.assertEqual(len(context["audits"]), 1)
         # Serialized for JS
-        import json
-
         self.assertIsInstance(context["audits"][0]["migrations"], str)
         self.assertEqual(json.loads(context["audits"][0]["host_labels"]), ["h0", "h1"])
         self.assertIn("current_cluster", context)
@@ -167,7 +165,7 @@ class ApiStatsTest(TestCase):
     def setUp(self):
         self.factory = RequestFactory()
 
-    @patch("dashboard.views._fetch_prometheus_metrics")
+    @patch("dashboard.views.fetch_dashboard_metrics")
     @patch("dashboard.views.get_flavor_list")
     @patch("dashboard.views.get_connection")
     def test_api_stats_returns_json_with_expected_keys(