PLT-4357 adding performance monitoring (#4622)

* WIP

* WIP

* Adding metrics collection

* updating vendor packages

* Adding metrics to config

* Adding admin console page for perf monitoring

* Updating glide

* switching to tylerb/graceful

vendor/github.com/prometheus/common/expfmt/testdata/json2

@@ -0,0 +1,46 @@
+[
+  {
+    "baseLabels": {
+      "__name__": "rpc_calls_total",
+      "job": "batch_job"
+    },
+    "docstring": "RPC calls.",
+    "metric": {
+      "type": "counter",
+      "value": [
+        {
+          "labels": {
+            "service": "zed"
+          },
+          "value": 25
+        },
+        {
+          "labels": {
+            "service": "bar"
+          },
+          "value": 24
+        }
+      ]
+    }
+  },
+  {
+    "baseLabels": {
+      "__name__": "rpc_latency_microseconds"
+    },
+    "docstring": "RPC latency.",
+    "metric": {
+      "type": "histogram",
+      "value": [
+        {
+          "labels": {
+            "service": "foo"
+          },
+          "value": {
+            "0.010000": 15,
+            "0.990000": 17
+          }
+        }
+      ]
+    }
+  }
+]