[DOCS] Adds explain DFA examples.

specification/ml/explain_data_frame_analytics/examples/200_response/MlExplainDataFrameAnalyticsResponseExample1.json

@@ -0,0 +1,39 @@
+{
+  "summary": "A succesful response for explaining a data frame analytics job configuration.",
+  "value": {
+    "field_selection": [
+      {
+        "field": "number_of_bedrooms",
+        "mappings_types": ["integer"],
+        "is_included": true,
+        "is_required": false,
+        "feature_type": "numerical"
+      },
+      {
+        "field": "postcode",
+        "mappings_types": ["text"],
+        "is_included": false,
+        "is_required": false,
+        "reason": "[postcode.keyword] is preferred because it is aggregatable"
+      },
+      {
+        "field": "postcode.keyword",
+        "mappings_types": ["keyword"],
+        "is_included": true,
+        "is_required": false,
+        "feature_type": "categorical"
+      },
+      {
+        "field": "price",
+        "mappings_types": ["float"],
+        "is_included": true,
+        "is_required": true,
+        "feature_type": "numerical"
+      }
+    ],
+    "memory_estimation": {
+      "expected_memory_without_disk": "128MB",
+      "expected_memory_with_disk": "32MB"
+    }
+  }
+}

specification/ml/explain_data_frame_analytics/examples/request/MlExplainDataFrameAnalyticsRequestExample1.json

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+{
+  "summary": "A request for explaining a data frame analytics job configuration.",
+  "value": {
+    "source": {
+      "index": "houses_sold_last_10_yrs"
+    },
+    "analysis": {
+      "regression": {
+        "dependent_variable": "price"
+      }
+    }
+  }
+}