rgw/role: separate dump_iam_role() for iam api

rgw/role: separate dump_iam_role() for iam api

create a new dump_iam_role() for iam api responses that dumps the subset
of role information presented by the apis

RGWRoleInfo::dump() and decode_json() are used by metadata sync to
transfer role metadata between zones, so must contain all information
about the role

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