[client-v2] Added session roles for client and operations

[chernser]

Summary

There is a feature and it should be supported by the new client. It allows to set roles for every operation where session may not be maintained (http requests are balanced between different DB instances).

!! Documentation should be updated also.

Closes: #1832

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials