Implement client sentiment retrieval

[rytis]

https://labs.ig.com/rest-trading-api-reference/service-detail?id=617
https://labs.ig.com/rest-trading-api-reference/service-detail?id=620
and perhaps: https://labs.ig.com/rest-trading-api-reference/service-detail?id=602

• Implement in client lib
• Implement in CLI tool