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` ?

{
        return session;
    }
    void updateSession(const Poco::URI & uri)
    {
        ++redirects;
        if (redirects <= max_redirects)
        {
            buildNewSession(uri);
        }
        else
        {
            throw Exception(ErrorCodes::TOO_MANY_REDIRECTS, "Too many redirects while trying to access {}", initial_uri.toString());
        }
    }
    virtual ~UpdatableSessionBase() = default;
};
namespace detail
{
    template <typename UpdatableSessionPtr>
    class ReadWriteBufferFromHTTPBase : public SeekableReadBufferWithSize
    {
    public:
        using HTTPHeaderEntry = std::tuple<std::string, std::string>;
        using HTTPHeaderEntries = std::vector<HTTPHeaderEntry>;
        
        struct Range