LU-16974 utils: lfs mirror resync to show progress

LU-16974 utils: lfs mirror resync to show progress

lfs mirror resync should be able to:
 - show progress like lfs mirror extend --stats does
 - throttle like lfs mirror extend -W does

use 64MB buffer for mirror resync by default.

Lustre-change: https://review.whamcloud.com/51750
Lustre-commit: TBD (from d03e56590243c2d854ce087e2fcb118ccb126d93)

Change-Id: Ibe60748542ff4a3731aa6a4a9907be82427a0ae9
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51878
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>