[Watcher] Use auto_expand_replicas on triggered_watches index too (elastic/x-pack-elasticsearch#3371)

In the previous pass, only the ".watch*" templates were impacted. This also should use `auto_expand_replicas`.

Original commit: elastic/x-pack-elasticsearch@5d3a4f1f7b

plugin/src/main/resources/triggered-watches.json

@@ -3,6 +3,7 @@
   "order": 2147483647,
   "settings": {
     "index.number_of_shards": 1,
+    "index.auto_expand_replicas": "0-1",
     "index.refresh_interval" : "-1",
     "index.format": 6,
     "index.priority": 900