LibreSSL support

Add LibreSSL support:

What does this mean? What have to be done on the Openfire side and what is not working?

Openfire uses the java implementation of SSL/TLS (JSSE), so there is no dependency on OpenSSL and so nothing to be done.

If openssl is mentioned in documentation it’s about certificate handling – AFAIK libressl’s cli tool is still called openssl, so there’s nothing to do in documentation either