fix(openapi): update kafka-mgmt/v1 OpenAPI document (#284)

Co-authored-by: app-services-ci <app-services-ci@users.noreply.github.com>

Author: app-services-ci

.openapi/kas-fleet-manager.yaml

@@ -1266,11 +1266,9 @@ components:
           description: 'Indicates whether there is capacity left per instance type'
           type: array
           items:
-            allOf:
-              - $ref: "#/components/schemas/RegionCapacityListItem"
+            $ref: "#/components/schemas/RegionCapacityListItem"
       required:
         - enabled
-        - supported_instance_types
         - capacity
     ServiceAccount:
       description: 'Service Account created in MAS-SSO for the Kafka Cluster for authentication'