doc/rgw: clarify path-style vs virtual-hosted-style access

doc/rgw: clarify path-style vs virtual-hosted-style access

instead of referring to "vhost-style", copy the "path-style" and
"virtual-hosted-style" language from https://docs.aws.amazon.com/AmazonS3/latest/userguide/VirtualHosting.html

expand the FQDN acronym to avoid potential confusion

"The second method is deprecated by AWS" had incorrectly referred to the
vhost-style method - clarify that it refers to path-style access

Signed-off-by: Casey Bodley <cbodley@redhat.com>