List active billing plans.

{  "items": [    {      "allows_flat_rate_cdn": true,      "code": "string",      "enforce_included_limit": true,      "invoiced": true,      "is_default": true,      "limits": {        "buildMaxConcurrent": 0,        "buildPriority": 0,        "functionBundleMaxBytes": 0,        "functionRequestMaxBytes": 0,        "functionResponseMaxBytes": 0,        "sourceMaxBytes": 0,        "sourceMaxFiles": 0,        "warmFloorBonus": 0,        "warmFloorMaxPerRegion": 0      },      "name": "string",      "requires_payment_method": true,      "sort_order": 0    }  ]}