mgr/cephadm: allow passing client/server cert/key in nvmeof spec

mgr/cephadm: allow passing client/server cert/key in nvmeof spec

Before this patch the client/server cert/key fields were
just filepaths that told the nvmeof gw daemon where to look
for the cert/key. There's not much reason why users would
care where in the nvmeof gw container the cert goes. It's more
useful to use these fields as a way to pass the certs/keys
to the daemon and then just hardcode where in the container
we'll place the certs/keys

Signed-off-by: Adam King <adking@redhat.com>
(cherry picked from commit e9fca39092348e6c08022341116875e831c175f0)