LU-17137 utils: Deprecate l_getidentity 'files' alias

LU-17137 utils: Deprecate l_getidentity 'files' alias

The use of 'files' masks the nss module files.
The psuedo module lustre should be used instead of files now.
The 'files' alias should be deprecated and a periodic warning
written (once per hour).

In addition a file /etc/lustre/perm.conf-warning created with
the warning that 'lookup lustre' should be used and 'files'
is deprecated.p

Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I8167c8827cb4e2120404c08c3f10220f13087a2f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52486
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>