CONNECT-IP (RFC 9484) support

*Title*:

Add support in Envoy for CONNECT-IP (RFC 9484)

*Description*:

Envoy has long supported [HTTP CONNECT](https://www.rfc-editor.org/rfc/rfc9110#section-9.3.6), a mechanism that allows tunneling the data stream inside TCP over an HTTP stream. Recently, support was added (#23564) for CONNECT-UDP ([RFC 9298](https://www.rfc-editor.org/rfc/rfc9298.html)), a similar mechanism that allows tunneling UDP (and subsequently QUIC and HTTP/3 connections) inside an HTTP stream.

We propose and plan to contribute similar Envoy support for CONNECT-IP. [RFC 9484](https://www.rfc-editor.org/rfc/rfc9484.html), Proxying IP in HTTP, colloquially and here referred to as “CONNECT-IP”, is a similar newly IETF-standardized protocol for tunneling IP packets over an HTTP stream. This functionality is generally useful to tunnel multi-transport data such as is needed to implement VPN connections.

See this [Design Document](https://docs.google.com/document/d/1uZbTbr807P95PXjgc72E-P8M54qKc_TlQ8iiy45fV5U/edit?usp=sharing) for our detailed plan.