ceph upgrade doc: add note about required configs
ceph upgrade doc: add note about required configs

Make users aware of the newly 'required' configs earlier in the upgrade
doc so they have more context when they arrive at the upgrade step to
consider changing these for their own clusters.

Signed-off-by: Blaine Gardner <135b86f2968bdbcc730c10d8ababd343bb675986@suse.com>

rook/rook,rook/rook,rook/rook,rook/nfs,rook/nfs,rook/rook,rook/rook,rook/nfs