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` ?

{
            Poco::Net::HTTPResponse response;
            call(response, method);
            if (initialization_error != InitializeError::NONE)
                return;
            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);
                saved_uri_redirect = uri_redirect;
            }
            if (withPartialContent() && response.getStatus() != Poco::Net::HTTPResponse::HTTPStatus::HTTP_PARTIAL_CONTENT)
            {
                
                if (read_range.begin)
                {
                    if (!exception)
                        exception = std::make_exception_ptr(
                            Exception(ErrorCodes::HTTP_RANGE_NOT_SATISFIABLE,
                                      "Cannot read with range: [{}, {}]", read_range.begin, read_range.end ? *read_range.end : '-'));
                    initialization_error = InitializeError::NON_RETRIABLE_ERROR;
                    return;
                }
                else if (read_range.end)
                {