Revert "set value required in constant_keyword field type (#419)"

This reverts commit 7e1a233.

Signed-off-by: dblock <dblock@amazon.com>

Author: dblock

CHANGELOG.md

@@ -83,7 +83,6 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Fixed query DSL `match` that supports a field name and value ([#405](https://github.com/opensearch-project/opensearch-api-specification/pull/405)) 
 - Fixed `/_mapping` with `index` in query ([#385](https://github.com/opensearch-project/opensearch-api-specification/pull/385))
 - Fixed duplicate `/_nodes/{node_id}` path ([#416](https://github.com/opensearch-project/opensearch-api-specification/pull/416))
-- Fixed required value for `constant_keyword` field type ([#419](https://github.com/opensearch-project/opensearch-api-specification/pull/419))
 
 ### Security
 

spec/schemas/_common.mapping.yaml

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