Reassign an agent
[Required authorization] Route required privileges: fleet-agents-all.
POST /api/fleet/agents/{agentId}/reassign
curl \ --request POST 'https://<KIBANA_URL>/api/fleet/agents/{agentId}/reassign' \ --header "Authorization: $API_KEY" \ --header "Content-Type: application/json" \ --header "kbn-xsrf: true" \ --data '{"policy_id":"string"}'