Support for custom url path

[radmirnovii]

Motivation:
Useful with http proxy. Previous version in ru.yandex.clickhouse has this feature with option USE_PATH_AS_DB=false.

current driver has WEB_CONTEXT option but it used only with trailing slash

[zhicwu]

Thank you @radmirnovii. Can we reuse web_context? I'm testing connection string with multiple hosts/URIs. Perhaps we can enhance the option to support both cases.

[radmirnovii]

Can we reuse web_context?
Do you want to just remove adding trailing slash in path?

[zhicwu]

Do you want to just remove adding trailing slash in path?

Yes. Web context should be also considered for health check like ping, because the url will be changed to http://host:port/<web_context>/ping. What's your scenario? I didn't see unit test there, so my guess was just arbitrary path without query or fragment, right?

Apologize for holding your PR for so long, I'll merge the 2 PRs with minor changes maybe, once I got load balancing performance issue fixed :<

[zhicwu]

Fixed in #956 along with some more tests.