doc/ceph-volume: add spillover fix procedure

doc/ceph-volume: add spillover fix procedure

Add a procedure that explains how, after an upgrade, to move bytes that
have spilled over to a relatively slow device back to the faster device.

This procedure was developed by Chris Dunlop on the [ceph-users] mailing
list, here: https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/message/POPUFSZGXR3P2RPYPJ4WJ4HGHZ3QESF6/

Eugen Block requested the addition of this procedure to the
documentation on 30 Aug 2024.

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 98618aaa1c8b786c7d240a210b62cc737fdb048d)