Alerting: Foundations of historian app. (#114463)

We have two historians in alerting - alert state and notification. The intention
of this app is to provide query capabilities for both.

In this initial commit, the existing /history API is simply cloned to the new
app. It is identical except that it will send Kubernetes-style error responses
instead of Grafana-style.

This approach was taken to implement the new app more iteratively - ideally we
would define a new API, but this requires quite a significant overhaul of the
backend code.

pkg/services/featuremgmt/toggles_gen.json

@@ -3633,4 +3633,4 @@
       }
     }
   ]
-}
+}