Add docs on Knative Serving autoscaling dashboard

Author: rh-max

_topic_map.yml

@@ -3215,6 +3215,8 @@ Topics:
     File: serverless-autoscaling-scale-bounds
   - Name: Concurrency
     File: serverless-autoscaling-concurrency
+  - Name: Autoscaling dashboard
+    File: serverless-autoscaling-dashboard
 #
 # Knative Eventing
 - Name: Knative Eventing

images/serverless-autoscaling-dashboard-activator-request-concurrency.png

@@ -0,0 +1,8 @@
+[id="serverless-autoscaling-dashboard-activator-metrics_{context}"]
+= Activator metrics
+
+The *Activator* graphs *Request Concurrency*, *Request Count by Response Code (last minute)*, and *Response Time (last minute)* show the timeline of requests going through the activator until the activator is removed from the request path. These graphs can be used, for example, to evaluate whether response count and the returned HTTP codes match expectations.
+
+image::serverless-autoscaling-dashboard-activator-request-concurrency.png[Activator: Request Concurrency]
+image::serverless-autoscaling-dashboard-activator-request-count.png[Activator: Request Count by Response Code (last minute)]
+image::serverless-autoscaling-dashboard-activator-response-time.png[Activator: Response Time (last minute)]