Update rest-api-spec

Author: pquentin

specification/_json_spec/indices.put_data_stream_settings.json

@@ -25,6 +25,11 @@
       ]
     },
     "params": {
+      "dry_run": {
+        "type": "boolean",
+        "description": "Perform a dry run but do not actually change any settings",
+        "default": false
+      },
       "timeout": {
         "type": "time",
         "description": "Specify timeout for acknowledging the cluster state update"