www/freeipa-auth-gssapi: Add new Port

mod_auth_gssapi is the Apache module FreeIPA uses for SPNEGO/GSSAPI
authentication of the Web UI and API. www/mod_auth_gssapi defaults to
the base-system GSSAPI on FreeBSD, which mixes base and ports MIT krb5
in one httpd process and breaks gssproxy interposition. This port is an
independent build hard-wired to the ports MIT krb5 (security/krb5) so it
matches the rest of the FreeIPA stack (net/freeipa-server,
security/gssproxy). It conflicts with ap24-mod_auth_gssapi.

Sponsored by: Netzkommune GmbH