List Agents

[  {    "agent_id": "string",    "tenant_id": "string",    "last_seen": "2019-08-24T14:15:22Z",    "active": true,    "invocations": 0,    "failed": 0,    "total_tokens": 0,    "estimated_cost_usd": "string",    "p50_latency_ms": 0,    "p95_latency_ms": 0  }]