Add subsystem metrics for the dispatcher (#13989)

This adds a handful of metrics to /api/v2/metrics/ recorded from the dispatcher main process

Adds logic in the dispatcher period tasks to calculate these for the last collection interval
Reports worker count, task count, scale up events, and availability

Add data to demo grafana dashboard

awx/main/dispatch/pool.py

@@ -339,6 +339,17 @@ class AutoscalePool(WorkerPool):
         # but if the task takes longer than the time defined here, we will force it to stop here
         self.task_manager_timeout = settings.TASK_MANAGER_TIMEOUT + settings.TASK_MANAGER_TIMEOUT_GRACE_PERIOD
 
+        # initialize some things for subsystem metrics periodic gathering
+        # the AutoscalePool class does not save these to redis directly, but reports via produce_subsystem_metrics
+        self.scale_up_ct = 0
+        self.worker_count_max = 0
+
+    def produce_subsystem_metrics(self, metrics_object):
+        metrics_object.set('dispatcher_pool_scale_up_events', self.scale_up_ct)
+        metrics_object.set('dispatcher_pool_active_task_count', sum(len(w.managed_tasks) for w in self.workers))
+        metrics_object.set('dispatcher_pool_max_worker_count', self.worker_count_max)
+        self.worker_count_max = len(self.workers)
+
     @property
     def should_grow(self):
         if len(self.workers) < self.min_workers:
@@ -443,7 +454,12 @@ class AutoscalePool(WorkerPool):
             idx = random.choice(range(len(self.workers)))
             return idx, self.workers[idx]
         else:
-            return super(AutoscalePool, self).up()
+            self.scale_up_ct += 1
+            ret = super(AutoscalePool, self).up()
+            new_worker_ct = len(self.workers)
+            if new_worker_ct > self.worker_count_max:
+                self.worker_count_max = new_worker_ct
+            return ret
 
     def write(self, preferred_queue, body):
         if 'guid' in body: