[client-v2] Async Configuration

[chernser]

Summary

Async execution doesn't help much if done inside the client. Application usually has better understanding how to organize threads. Handling async code is more complex and hides some issues.

What will be changed:

• async configuration applied to a client v2. By default request will be executed in the same thread.

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

[sonarcloud]

Quality Gate failed

Failed conditions
60.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud