LU-11048 docs: adding missing pool man pages

LU-11048 docs: adding missing pool man pages

Adding lctl-pool_destroy.8, lctl-pool_list.8 and lctl-pool_remove.8.

Test-Parameters: trivial
Signed-off-by: Frederick Dilger <fdilger@whamcloud.com>
Change-Id: I227a85b9703346a7bce4250670002c97c2d37cb8
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56303
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sergey Cheremencev <scherementsev@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>