Support connect-udp with MASQUE

Naiveproxy is using QUIC DATAGRAM for connect-udp. Is it possible to support tunneling udp over MASQUE, that is in the following: ```txt :method: CONNECT :protocol: connect-udp :scheme: https :authority: proxy.example.com :path: /.well-known/masque/udp/{target_host}/{target_port}/ capsule-protocol: ?1 ``` This can carry capsule datagrams over h2/h3 when quic datagram is unavailable. This is defined in RFC 9298. ```txt HTTP DATA stream: +--------------+----------------+--------------------+ | Capsule Type | Capsule Length | Capsule Value | +--------------+----------------+--------------------+ Capsule Value for DATAGRAM: +------------+-------------+ | Context ID | UDP payload | +------------+-------------+ ``` Context ID and Capsule Type are `0x00`, capsule length is quic varint.