Create configuration set

{
  "name": "production",
  "description": "Production transactional sends",
  "customer_id": "cust_550e8400-...",
  "sending_enabled": true,
  "reputation_tracking_enabled": true,
  "suppression_options": "BOUNCE_AND_COMPLAINT",
  "tags": { "env": "prod", "team": "platform" }
}

{
  "success": true,
  "configuration_set": {
    "config_set_id": "cs_550e8400-...",
    "name": "production",
    ...
  }
}