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` ?

exception = nullptr;
                    break;
                }
                catch (const Poco::Exception & e)
                {
                    /**
                     * Retry request unconditionally if nothing has been read yet.
                     * Otherwise if it is GET method retry with range header.
                     */
                    bool can_retry_request = !offset_from_begin_pos || method == Poco::Net::HTTPRequest::HTTP_GET;
                    if (!can_retry_request)
                        throw;
                    LOG_ERROR(log,
                              "HTTP request to `{}` failed at try {}/{} with bytes read: {}/{}. "
                              "Error: {}. (Current backoff wait is {}/{} ms)",
                              uri.toString(), i + 1, settings.http_max_tries,
                              getOffset(), read_range.end ? toString(*read_range.end) : "unknown",
                              e.displayText(),
                              milliseconds_to_wait, settings.http_retry_max_backoff_ms);
                    retry_with_range_header = true;
                    exception = std::current_exception();
                    impl.reset();
                    auto http_session = session->getSession();
                    http_session->reset();
                    sleepForMilliseconds(milliseconds_to_wait);
                }
                milliseconds_to_wait = std::min(milliseconds_to_wait * 2, settings.http_retry_max_backoff_ms);
            }
            if (exception)
                std::rethrow_exception(exception);