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` ?

#pragma once
#include <functional>
#include <base/types.h>
#include <base/sleep.h>
#include <IO/ConnectionTimeouts.h>
#include <IO/HTTPCommon.h>
#include <IO/ReadBuffer.h>
#include <IO/ReadBufferFromIStream.h>
#include <IO/ReadHelpers.h>
#include <IO/ReadSettings.h>
#include <Poco/Any.h>
#include <Poco/Net/HTTPBasicCredentials.h>
#include <Poco/Net/HTTPClientSession.h>
#include <Poco/Net/HTTPRequest.h>
#include <Poco/Net/HTTPResponse.h>
#include <Poco/URI.h>
#include <Poco/Version.h>
#include <Common/DNSResolver.h>
#include <Common/RemoteHostFilter.h>
#include <Common/config.h>
#include <base/logger_useful.h>
#include <Poco/URIStreamFactory.h>
namespace ProfileEvents
{
    extern const Event ReadBufferSeekCancelConnection;
}
namespace DB
{