Add support for the RFC7250 certificate-type extensions.
Alows the use of only private keys for connection (i.e. certs not needed).
Add APIs
Add unit tests
Add documentation
Add s_client/s_server support
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18185)
