Merge thing command at /policyId

{
  "topic": "org.eclipse.ditto/fancy-thing/things/twin/commands/merge",
  "headers": {
    "content-type": "application/merge-patch+json",
    "correlation-id": "<command-correlation-id>"
  },
  "path": "/policyId",
  "value": "org.eclipse.ditto:the_policy_id"
}