abstractions/authentication: Add GSSAPI mechanism modules config

Daniel Richard G. requested to merge iskunk/apparmor:feature/auth-update into master

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)

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