etc/mtree: Add package tags for Kerberos directories

Fixes: e7e7bf757ace ("krb5: create the KDC database directory")
MFC after: 3 seconds
Reviewed by: cy
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D52975

(cherry picked from commit 6235ee2848df583d600a7b5d7cc284a5b32c7be7)