doc: Updates information for SSL configuration in Ceph Object Gateway installation.

Signed-off-by: Nilamdyuti Goswami <ngoswami@redhat.com>
Merge pull request #3260 from nilamdyuti/wip-doc-ceph-object-gateway

doc: Updates information for SSL configuration in Ceph Object Gateway installation.

Reviewed-by: John Wilkins <jowilkin@redhat.com>