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` ?

{
            next_callback = next_callback_;
            
            next_callback(count());
        }
        const std::string & getCompressionMethod() const
        {
            return content_encoding;
        }
    };
}
class UpdatableSession : public UpdatableSessionBase<HTTPSessionPtr>
{
    using Parent = UpdatableSessionBase<HTTPSessionPtr>;
public:
    UpdatableSession(
        const Poco::URI uri,
        const ConnectionTimeouts & timeouts_,
        const UInt64 max_redirects_)
        : Parent(uri, timeouts_, max_redirects_)
    {
        session = makeHTTPSession(initial_uri, timeouts);
    }
    void buildNewSession(const Poco::URI & uri) override
    {
        session = makeHTTPSession(uri, timeouts);
    }
};
class ReadWriteBufferFromHTTP : public detail::ReadWriteBufferFromHTTPBase<std::shared_ptr<UpdatableSession>>