docs: Fix data_connector schema fields to match API response

[ellicenelson]

Why?

The data_connector schema in the Unstable OpenAPI spec has fields that don't match the actual API response. The API returns direct_fin_usage (boolean), created_by_admin_id, and updated_by_admin_id, but the schema documents usage (string enum) and omits the admin ID fields.

How?

Replaces usage with direct_fin_usage in the schema and example response. Adds created_by_admin_id and updated_by_admin_id fields.

Companion PR:

• https://github.com/intercom/developer-docs/pull/780

_{Generated with Claude Code}