Add CPU throttling indicator

Add an indicator of whether the CPU has been throtting (usually due
to thermal constraints) to the host dashboard, overlaid on top of
the CPU usage graph as a red line.

roles/float-infra-prometheus/templates/grafana/dashboards/host.json

@@ -132,6 +132,28 @@
                 }
               }
             ]
+          },
+          {
+            "matcher": {
+              "id": "byName",
+              "options": "throttle"
+            },
+            "properties": [
+              {
+                "id": "color",
+                "value": {
+                  "fixedColor": "red",
+                  "mode": "fixed"
+                }
+              },
+              {
+                "id": "custom.stacking",
+                "value": {
+                  "group": "A",
+                  "mode": "none"
+                }
+              }
+            ]
           }
         ]
       },
@@ -190,6 +212,20 @@
           "legendFormat": "{{mode}} ",
           "refId": "B",
           "step": 45
+        },
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "P49960DE5880E8C68"
+          },
+          "editorMode": "code",
+          "expr": "sum(irate(node_cpu_core_throttles_total{host=~\"$server\"}[$__rate_interval])) > bool 0 > 0",
+          "hide": false,
+          "instant": false,
+          "interval": "5m",
+          "legendFormat": "throttle",
+          "range": true,
+          "refId": "C"
         }
       ],
       "title": "CPU: utilization",
@@ -2853,4 +2889,4 @@
   "uid": "W8eE_Qgik",
   "version": 4,
   "weekStart": ""
-}
+}
\ No newline at end of file