LU-17432 libcfs: new CDEBUG_SLOW message type

LU-17432 libcfs: new CDEBUG_SLOW message type

Created new CDEBUG_SLOW message type that will skip the first
SECONDS of messages, then continue printing to console as normal.

Specifically CWARN_SLOW and CERROR_SLOW have been created which
mirror the functionality of their respective CWARN and CERROR
functions but with the additional SLOW behavior.

Signed-off-by: Frederick Dilger <fdilger@whamcloud.com>
Change-Id: I905fdff795488ff937faf4d04d5d3d6fec24950a
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55439
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>