Some URLs expect a User-Agent header.

Example (version 22.2.1.3767):
```sql
SELECT * FROM url('https://api.github.com/users/clickhouse','JSONAsString');
```
Results in:
```
Code: 86. DB::Exception: Received error from remote server /users/clickhouse. HTTP status code: 403 Forbidden, body: 
Request forbidden by administrative rules. Please make sure your request has a User-Agent header (http://developer.github.com/v3/#user-agent-required). Check https://developer.github.com for other possible causes.
: While executing URL. (RECEIVED_ERROR_FROM_REMOTE_IO_SERVER) (version 22.2.1.3767)
```

Maybe it's nice to always send a header along, something like `User-Agent: ClickHouse/22.2.1.3767` ?

{
            if (read_range.end)
                return *read_range.end - read_range.begin;
            Poco::Net::HTTPResponse response;
            for (size_t i = 0; i < 10; ++i)
            {
                try
                {
                    call(response, Poco::Net::HTTPRequest::HTTP_HEAD);
                    while (isRedirect(response.getStatus()))
                    {
                        Poco::URI uri_redirect(response.get("Location"));
                        remote_host_filter.checkURL(uri_redirect);
                        session->updateSession(uri_redirect);
                        istr = callImpl(uri_redirect, response, method);
                    }
                    break;
                }
                catch (const Poco::Exception & e)
                {
                    LOG_ERROR(log, "Failed to make HTTP_HEAD request to {}. Error: {}", uri.toString(), e.displayText());
                }
            }
            if (response.hasContentLength())
                read_range.end = read_range.begin + response.getContentLength();
            return read_range.end;
        }
        enum class InitializeError