Upsert agent integration

{
  "success": true,
  "data": {
    "id": "your-integration-id",
    "account_id": "your-account-id",
    "agent_id": "your-agent-id",
    "provider": "whatsapp",
    "config": {
      "phone_number": "+5511999999999",
      "instance_name": "my-instance"
    },
    "created_at": "2024-01-15T10:30:00Z",
    "updated_at": "2024-01-15T10:30:00Z"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z"
  }
}

{
  "success": false,
  "error": {
    "code": "BAD_REQUEST",
    "message": "Invalid input data"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z",
    "path": "/api/v1/agents/{id}/integrations",
    "method": "POST"
  }
}

{
  "success": false,
  "error": {
    "code": "UNAUTHORIZED",
    "message": "Invalid or missing authentication token"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z",
    "path": "/api/v1/agents/{id}/integrations",
    "method": "POST"
  }
}

{
  "success": false,
  "error": {
    "code": "FORBIDDEN",
    "message": "Insufficient permissions to perform this action"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z",
    "path": "/api/v1/agents/{id}/integrations",
    "method": "POST"
  }
}

{
  "success": false,
  "error": {
    "code": "NOT_FOUND",
    "message": "Agent not found"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z",
    "path": "/api/v1/agents/{id}/integrations",
    "method": "POST"
  }
}

{
  "success": false,
  "error": {
    "code": "INTERNAL_SERVER_ERROR",
    "message": "An unexpected error occurred"
  },
  "meta": {
    "timestamp": "2024-01-15T10:30:00Z",
    "path": "/api/v1/agents/{id}/integrations",
    "method": "POST"
  }
}