set value required in constant_keyword field type

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

spec/schemas/_common.mapping.yaml

@@ -789,13 +789,14 @@ components:
         - type: object
           properties:
             value:
-              type: object
+              type: string
             type:
               type: string
               enum:
                 - constant_keyword
           required:
             - type
+            - value
     FieldAliasProperty:
       allOf:
         - $ref: '#/components/schemas/PropertyBase'

tests/mapping/constant_keyword.yaml

@@ -0,0 +1,33 @@
+$schema: ../../json_schemas/test_story.schema.yaml
+
+description: Test constant_keyword field type and retrieving a doc.
+
+prologues:
+  - path: /{index}
+    method: PUT
+    parameters:
+      index: movies
+    request_body:
+      payload:
+        mappings:
+          properties:
+            genre:
+              type: constant_keyword
+              value: Romantic comedy
+
+epilogues:
+  - path: /movies
+    method: DELETE
+    status: [200, 404]
+chapters:
+  - synopsis: Create a document.
+    path: /{index}/_doc
+    method: POST
+    parameters:
+      index: movies
+    request_body:
+      payload:
+        genre: Romantic comedy
+        year: 1991
+    response:
+      status: 201