Add test about nested aggregation

Signed-off-by: kkewwei <[email protected]>
Signed-off-by: kewei.11 <[email protected]>

tests/default/_core/search/aggs/nested_agg.yaml

@@ -0,0 +1,96 @@
+$schema: ../../../../../json_schemas/test_story.schema.yaml
+
+description: Test aggregation.
+prologues:
+  - path: user_infos
+    method: PUT
+    request_body:
+      payload:
+        mappings:
+          properties:
+            user:
+              type: nested
+              properties:
+                name:
+                  type: keyword
+                address:
+                  type: nested
+                  properties:
+                    city:
+                      type: nested
+                      properties:
+                        country:
+                          type: keyword
+  - path: /_bulk
+    method: POST
+    request_body:
+      content_type: application/x-ndjson
+      payload:
+        - {index: {_index: user_infos, _id: '0'}}
+        - {user: {name: user1, address: {city: {country: country1}}}}
+        - {index: {_index: user_infos, _id: '1'}}
+        - {user: {name: user2, address: {city: {country: country2}}}}
+chapters:
+  - synopsis: aggregation with nested.
+    path: /user_infos/_search
+    method: POST
+    request_body:
+      payload:
+        size: 0
+        aggregation:
+          nested_agg:
+            nested:
+              path: user
+            aggregation:
+              a_b1:
+                terms:
+                  field: user.name
+                aggregation:
+                  city:
+                    nested:
+                      path: user.address.city
+                    aggregation:
+                      country:
+                        terms:
+                          field: user.address.city.country
+    response:
+      status: 200
+      payload:
+        timed_out: false
+        hits:
+          total:
+            value: 2
+            relation: eq
+          hits: []
+        aggregations:
+          nested_agg:
+            doc_count: 2
+            a_b1:
+              doc_count_error_upper_bound: 0
+              sum_other_doc_count: 0
+              buckets:
+                - key: user1
+                  doc_count: 1
+                  city:
+                    doc_count: 1
+                    country:
+                      doc_count_error_upper_bound: 0
+                      sum_other_doc_count: 0
+                      buckets:
+                        - key: country1
+                          doc_count: 1
+                - key: user2
+                  doc_count: 1
+                  city:
+                    doc_count: 1
+                    country:
+                      doc_count_error_upper_bound: 0
+                      sum_other_doc_count: 0
+                      buckets:
+                        - key: country2
+                          doc_count: 1
+
+epilogues:
+  - path: /user_infos
+    method: DELETE
+    status: [200, 404]