[client-v2] Added setting log_comment

[chernser]

Summary

There is an option to set a comment that will be seen in system.query_log record associated with a query. It is useful for troubleshooting. In case of HTTP interface client should send the comment thru query parameter log_comment.

Closes: #1836

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

[mzitnik]

Looks like Query & Insert Settings share some variables do you think we should extract a common base for team?

[chernser]

Thanks @mzitnik! I've replaced code with shared constant from ClientSettings.

[mzitnik]

Thanks @mzitnik! I've replaced code with shared constant from ClientSettings.

Actually was referring if we can have a common base class since there is shared code

[sonarcloud]

Quality Gate failed

Failed conditions
50.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud

[chernser]

@mzitnik I think, we should not do it to keep developer away from idea of extracting common part.
I do not plan to add all server settings in such way and it should not be a problem for maintenance. What I'm afraid of that joining two separate mechanisms will lead to more rigid code and it will not save time as intendent.