LU-17053 libcfs: make a debugfs equivalent for markers

LU-17053 libcfs: make a debugfs equivalent for markers

Most of the ioctl handlding that was LNet related has been moved
from libcfs to LNet. One left over are markers which allow
injection of strings into the lustre debug buffer located in
libcfs_ioctl(). This is the only functionality which exist in
libcfs yet it is only available in lnet module. We can create
an debugfs equivalent that also allows injection of strings
into the Lustre debug buffers with scripts.

Change-Id: I22395b6b19f94de3c95ba8517a14d2ea251fe37a
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54363
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>