sh: Add config tag to /.profile

The file /.profile is installed as a hard link to /root/.profile. The
file in /root has the config tag, but the file in / does not, which
causes it to be overwritten by pkg upgrade. Since they're linked, this
also overwrites the file in /root.

Add the config tag to the file in / as well, so pkg treates both links
as config files and won't overwrite them.

PR: 289097
MFC after: 3 days
Reviewed by: bapt, emaste
Differential Revision: https://reviews.freebsd.org/D52162