rgw: support 1+ rgw instance in `radosgw_frontend_port`

rgw: support 1+ rgw instance in `radosgw_frontend_port`

Change the radosgw_frontend_port to take in account more than 1 RGW instance,
in it's original form `radosgw_frontend_port: radosgw_frontend_port | int`,
it configured the 8080 port to all instances, with the following modification
`radosgw_frontend_port: radosgw_frontend_port | int + item|int` we increase in
1 the port count.

Co-authored-by: Daniel Parkes <dparkes@redhat.com>
Signed-off-by: raul <rmahique@redhat.com>