[Data-Frame] make the config be strictly parsed on _preview (#39713)

* [Data-Frame] make the config be strictly parsed on _preview

* adding test to verify strictly parsing

* adjusting test after master merge

Author: benwtrent

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/dataframe/action/PreviewDataFrameTransformAction.java

@@ -65,7 +65,7 @@ public static Request fromXContent(final XContentParser parser) throws IOExcepti
                     .createParser(parser.getXContentRegistry(),
                         LoggingDeprecationHandler.INSTANCE,
                         BytesReference.bytes(xContentBuilder).streamInput())) {
-                return new Request(DataFrameTransformConfig.fromXContent(newParser, "transform-preview", true));
+                return new Request(DataFrameTransformConfig.fromXContent(newParser, "transform-preview", false));
             }
         }
 

x-pack/plugin/src/test/resources/rest-api-spec/test/data_frame/preview_transforms.yml

@@ -88,3 +88,17 @@ setup:
   - match: { preview.2.airline: foo }
   - match: { preview.2.by-hour: "2017-02-49 01" }
   - match: { preview.2.avg_response: 42.0 }
+
+---
+"Test preview transform with invalid config":
+  - do:
+      catch: /\[data_frame_terms_group\] unknown field \[not_a_terms_param\]/
+      data_frame.preview_data_frame_transform:
+        body: >
+          {
+            "source": "airline-data",
+            "pivot": {
+              "group_by": {"airline": {"terms": {"not_a_terms_param": "airline"}}},
+              "aggs": {"avg_response": {"avg": {"field": "responsetime"}}}
+            }
+          }