[ech] PR with ECH API design doc

[Stephen Farrell]

Hiya,

I got a suggestion that it might be useful to create a PR where ECH API 
designs could be discussed so I did that. [1]

Comments welcome there!
Thanks,
S.

[1] https://github.com/openssl/openssl/pull/20408
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_0xE4D8E9F997A833DD.asc
Type: application/pgp-keys
Size: 1197 bytes
Desc: OpenPGP public key
URL: <https://mta.openssl.org/pipermail/ech/attachments/20230301/7c3f7966/attachment.asc>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 236 bytes
Desc: OpenPGP digital signature
URL: <https://mta.openssl.org/pipermail/ech/attachments/20230301/7c3f7966/attachment.sig>