Remove all gogoproto extensions

This commit removes the following gogoproto extensions;

- gogoproto.nullable
- gogoproto.customename
- gogoproto.unmarshaller_all
- gogoproto.stringer_all
- gogoproto.sizer_all
- gogoproto.marshaler_all
- gogoproto.goproto_unregonized_all
- gogoproto.goproto_stringer_all
- gogoproto.goproto_getters_all

None of them are supported by Google's toolchain (see #6564).

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

namespaces.go

@@ -38,7 +38,7 @@ type remoteNamespaces struct {
 func (r *remoteNamespaces) Create(ctx context.Context, namespace string, labels map[string]string) error {
 	var req api.CreateNamespaceRequest
 
-	req.Namespace = api.Namespace{
+	req.Namespace = &api.Namespace{
 		Name:   namespace,
 		Labels: labels,
 	}
@@ -66,7 +66,7 @@ func (r *remoteNamespaces) Labels(ctx context.Context, namespace string) (map[st
 func (r *remoteNamespaces) SetLabel(ctx context.Context, namespace, key, value string) error {
 	var req api.UpdateNamespaceRequest
 
-	req.Namespace = api.Namespace{
+	req.Namespace = &api.Namespace{
 		Name:   namespace,
 		Labels: map[string]string{key: value},
 	}