Add template config for Beat state to X-Pack Monitoring (elastic#31809)

With elastic/beats#7075 Beats introduces state reporting for X-Pack Monitoring. The data sent up to Elasticsearch ends up stored in the following format.

```
"beats_state": {
  "timestamp": "2018-07-05T07:21:03.581Z",
  "state": {
    "module": {
      "count": 1,
      "names": [
        "http"
      ]
    }
  },
  "beat": {
    "uuid": "594039b5-6353-4d78-9bad-778ecc0fe83f",
    "type": "metricbeat",
    "version": "7.0.0-alpha1",
    "name": "ruflin",
    "host": "ruflin"
  }
}
```

This PR adds the new fields to the template.

Author: ruflin

x-pack/plugin/core/src/main/resources/monitoring-beats.json

@@ -14,6 +14,47 @@
     "doc": {
       "dynamic": false,
       "properties": {
+        "beats_state": {
+          "properties": {
+            "beat": {
+              "properties": {
+                "host": {
+                  "type": "keyword"
+                },
+                "name": {
+                  "type": "keyword"
+                },
+                "type": {
+                  "type": "keyword"
+                },
+                "uuid": {
+                  "type": "keyword"
+                },
+                "version": {
+                  "type": "keyword"
+                }
+              }
+            },
+            "state": {
+              "properties": {
+                "module": {
+                  "properties": {
+                    "count": {
+                      "type": "long"
+                    },
+                    "names": {
+                      "type": "keyword"
+                    }
+                  }
+                }
+              }
+            },
+            "timestamp": {
+              "format": "date_time",
+              "type": "date"
+            }
+          }
+        },
         "beats_stats": {
           "properties": {
             "beat": {