Rename `configapi.GroupVersion` to `SchemeGroupVersion` for consistency

[efiacor]

Status: Not started

api/porchconfig/v1alpha1 exports its group version as GroupVersion, while the other API packages (api/porch/v1alpha1, api/porch/v1alpha2) use the Kubernetes convention SchemeGroupVersion. Visible when the three appear side by side, e.g. in internal/cliutils/client_v1alpha2.go:

rm := meta.NewDefaultRESTMapper([]schema.GroupVersion{
    porchv1alpha2.SchemeGroupVersion,
    porchapi.SchemeGroupVersion,
    configapi.GroupVersion,          // odd one out
})

Fix: rename GroupVersion → SchemeGroupVersion in api/porchconfig/v1alpha1/groupversion_info.go and update ~20 references across the codebase. Public symbol — technically a breaking change for external importers, but configapi has few (if any) downstream consumers.

Acceptance Criteria:

• GroupVersion renamed to SchemeGroupVersion in api/porchconfig/v1alpha1
• All ~20 references updated
• All tests pass