Support ECH Split Mode

Hi, I'd like to set up a Caddy-l4 server to accept ECH, and do SNI/QUIC-SNI routing based on the decrypted Inner ClientHello without terminating TLS. I believe this makes Caddy-l4 act as a client-facing server in the Split Mode topology of the draft spec.

I'd like to ask: could it be some day supported in Caddy-L4?

I guess this would probably involve reading SNI matchers for the anonymity set, and remove certs management entirely from Caddy-L4's side. Though I'm not qualified to speak of implementation details

Please let me know if this can be possible, thanks in advance

---

Further thoughts (just leaving them here if that's okay): redacted because they're rubbish