earlier, we had the issue for osd placement regarding
whether we should merge the placements or not.
Now, we have option `skipApplyAllPlacement` to
enable/disable osd placement. By default it is false
which means it will merge both placement.All() and
storageClassDeviceSets.Placement, when true
it will only apply storageClassDeviceSets.Placement.
Also, adding unit test.
Closes: https://github.com/rook/rook/issues/8135
Signed-off-by: subhamkrai <srai@redhat.com>