GET /v3/instruments/:id/private-instruments

List private-market instruments owned by a reporting entity. The `:id`
here is a *reporting entity* ID, not an instrument ID.

Path params:
  id (required) — Reporting entity identifier (Mongo ObjectID).

Response (200 OK):
{
  "data": [
    {
      "id": "string",
      "type": "private-market-fund-commitment-based-instrument",
      "attributes": { /* see the per-type instrument spec */ },
      "relationships": { /* see the per-type instrument spec */ }
    }
  ]
}