New "restricted" risk rating value on country info

Broker API

Adds restricted to the country risk rating enums and clarifies the country info response documentation.

• crypto_risk_rating and securities_risk_rating on the country info schema can now return restricted.
• The 200 response example now shows ISO 3166-1 alpha-3 country codes as top-level keys, matching the dictionary shape the endpoint actually returns.

Affected Endpoints

• GET /v1/country-info