Extend the product `type` to be able to describe orders in more detail

## Enhancement Request

### Use Case:
Add field to support further descriptive information of a product `type`.

**Example:**
```json
{
"type": "fdc3.trade",
"name": "FLY vs 530",
"notes": "New Trade",
"product": {
"type": "fdc3.product",
"id": {
"productId": "Sep24 350/400/450",
"type": "CALL"
},
"instrument": {
"type": "fdc3.instrument",
"id": {
"ticker": "QQQ US"
}
}
}
}
```

### Workflow Description
Ability to send supporting information around a product type.

Comments and feedback welcomed.

No file, test, or entry point is named. Start by locating the existing product type definition and related specification examples, then clarify whether fields such as name and notes are intended and what compatibility requirements apply; done means the agreed shape is consistently specified and validated.

Written by the indexing model from the issue text.