ceph-volume: lvm.Lvm.setup_metadata_devices refactor

ceph-volume: lvm.Lvm.setup_metadata_devices refactor

This commit refactors setup_metadata_devices into smaller helper methods.
It keeps the distinction between existing logical volumes and raw devices
explicit, centralizes tag handling and path assignment to make the
control flow obvious and separates responsibilities for checking, creating,
and tagging devices.

Fixes: https://tracker.ceph.com/issues/73445
Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>