Add unqualified_reason_id to Deal firehose API

Feature Request Summary: 

Zendesk Sell deals firehose API endpoint should have every field that the Core API deals endpoint has. Right now, the firehose API doesn't not have every field that the core API has. For example, the firehose API is missing the unqualified_reason_id for deals.

Description/Use Cases: 

An application continuously consumes from the deals firehose API endpoint (/v3/deals/stream) and actions are triggered on certain changes. One of these actions requires the unqualified reason. Since the unqualified_reason_id is missing, the app has to do an additional lookup at the deals endpoint (v2/deals) to get the unqualified_reason_id field. 

With this workaround, the application doesn't know what the unqualified_reason was before it was changed.

Business impact of limitation or missing feature:

We aren't able to track the unqualified_reasons using the deals firehose API, which is valuable for gathering data and monitoring why deals were unqualified.