abstractions/authentication: Add GSSAPI mechanism modules config
Found in testing a slimmed-down usr.sbin.sshd
profile:
Jun 8 21:09:37 testvm kernel: [ 54.770501] audit: type=1400 audit(1686272977.933:67): apparmor="DENIED" operation="open" profile="/usr/sbin/sshd" name="/etc/gss/mech.d/" pid=1036 comm="sshd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
(Reference for GSSAPI mechanism modules)