Set SchemaContract.Document as required. (#20110)

* Updated documentation of the SchemaContract. Server use to return code 500 in case SchemaContract.Document is null. That issue was fixed in the APIM and server will return proper response code.

* Fix AzureApiValidation

* update field with properties

Author: agapovm

specification/apimanagement/resource-manager/Microsoft.ApiManagement/preview/2022-04-01-preview/definitions.json

@@ -5753,7 +5753,8 @@
         }
       },
       "required": [
-        "contentType"
+        "contentType",
+        "document"
       ],
       "description": "API Schema create or update contract Properties."
     },