tls-server-end-point support

[Neustradamus]

Dear @strophe team, @sjaeckel and all other devs of the World,

You have done a good work recently with the -PLUS variants support with "tls-unique" (a part of RFC5929), "tls-exporter" (RFC9266), thanks a lot for this adding @sjaeckel.

Can you add the missing "tls-server-end-point" support in libstrophe?

It is needed in several XEPs, and next SASL2 (IETF I-D: draft-melnikov-sasl2).

Some links:

• RFC5929: Channel Bindings for TLS: https://datatracker.ietf.org/doc/html/rfc5929 -> https://datatracker.ietf.org/doc/html/rfc5929#section-4
• XEP-0388: Extensible SASL Profile: https://xmpp.org/extensions/xep-0388.html
• XEP-0440: SASL Channel-Binding Type Capability: https://xmpp.org/extensions/xep-0440.html
• XEP-0474: SASL SCRAM Downgrade Protection: https://xmpp.org/extensions/xep-0474.html
• XEP-0480: SASL Upgrade Tasks: https://xmpp.org/extensions/xep-0480.html
• IETF I-D: draft-melnikov-sasl2: Extensible Simple Authentication and Security Layer (SASL): https://datatracker.ietf.org/doc/html/draft-melnikov-sasl2
• State of Play scram-sasl/info#1

Thanks in advance.