LU-930 doc: add lctl-lcfg man pages

LU-930 doc: add lctl-lcfg man pages

Add "lctl lcfg_clear", "lctl lcfg_erase", and "lctl lcfg_fork"
as aliases for "clear_conf", "erase_lcfg", and "fork_lcfg"
respectively, for more consitent naming.

Add separate man pages for lctl-lcfg_clear, lctl-lcfg_erase,
lcfg-lcfg_fork, lctl-erase_lcfg, lctl-fork_lcfg, lctl-clear_conf.

Remove the combined man page for lctl-lcfg.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I9daf2efc0cf0f9a2b549d8513098729151178207
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48887
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>