There have been some changes for Compute V2 Server Groups API: https://docs.openstack.org/nova/stein/reference/api-microversion-history.html#id58

Gophercloud should support policy and optional rules fields in structs of the compute/v2/extensions/servergroups package.

Docs: https://developer.openstack.org/api-ref/compute/#server-groups-os-server-groups