Insert ephemeral IDs + correct pipeline event stats into the logstash_stats document (elastic/x-pack-elasticsearch#1747)

Before the event stats were mislabeled, so were not being indexed, and
the ephemeral_id was only in the _state document.

Original commit: elastic/x-pack-elasticsearch@ca0ec81aa5

plugin/src/main/resources/monitoring-logstash.json

@@ -50,6 +50,9 @@
                 "name": {
                   "type": "keyword"
                 },
+                "ephemeral_id": {
+                  "type": "keyword"
+                },
                 "host": {
                   "type": "keyword"
                 },
@@ -245,15 +248,18 @@
                 "hash": {
                   "type": "keyword"
                 },
+                "ephemeral_id": {
+                  "type": "keyword"
+                },
                 "events": {
                   "properties": {
-                    "input": {
+                    "in": {
                       "type": "long"
                     },
-                    "filter": {
+                    "filtered": {
                       "type": "long"
                     },
-                    "output": {
+                    "out": {
                       "type": "long"
                     }
                   }