Inhibit info alerts unless other alerts fire (#1507)

* Inhibit info alerts unless other alerts fire

* Fix nits

manifests/alertmanager-secret.yaml

@@ -28,10 +28,17 @@ stringData:
       - "severity = warning"
       "target_matchers":
       - "severity = info"
+    - "equal":
+      - "namespace"
+      "source_matchers":
+      - "alertname = InfoInhibitor"
+      "target_matchers":
+      - "severity = info"
     "receivers":
     - "name": "Default"
     - "name": "Watchdog"
     - "name": "Critical"
+    - "name": "null"
     "route":
       "group_by":
       - "namespace"
@@ -43,6 +50,9 @@ stringData:
       - "matchers":
         - "alertname = Watchdog"
         "receiver": "Watchdog"
+      - "matchers":
+        - "alertname = InfoInhibitor"
+        "receiver": "null"
       - "matchers":
         - "severity = critical"
         "receiver": "Critical"