* [IO] HTTP User-Agent header
Added HTTP User-Agent Header to HTTP requests.
User-Agent: ClickHouse/VERSION_STRING
Input header vectors could potentially contain User-Agent. If so, do not set another.
* [Tests] HTTP User Agent
Added stateless functional test 02205_HTTP_user_agent.
Co-authored-by: Filatenkov Artur <58165623+FArthur-cmd@users.noreply.github.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
