func (s *GroupClustersService) ListClusters(pid interface{}, options ...RequestOptionFunc) ([]*GroupCluster, *Response, error) {
	group, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("groups/%s/clusters", pathEscape(group))
	req, err := s.client.NewRequest(http.MethodGet, u, nil, options)
	if err != nil {
		return nil, nil, err
	}
	var pcs []*GroupCluster
	resp, err := s.client.Do(req, &pcs)
	if err != nil {
		return nil, resp, err
	}
	return pcs, resp, err
}
ListClusters gets a list of all clusters in a group.

GitLab API docs:
https://docs.gitlab.com/ee/api/group_clusters.html#list-group-clusters
package gitlab
import (
	"fmt"
	"net/http"
	"time"
)
type GroupClustersService struct {
	client *Client
}
type GroupCluster struct {
	ID                 int                 `json:"id"`
	Name               string              `json:"name"`
	Domain             string              `json:"domain"`
	CreatedAt          *time.Time          `json:"created_at"`
	ProviderType       string              `json:"provider_type"`
	PlatformType       string              `json:"platform_type"`
	EnvironmentScope   string              `json:"environment_scope"`
	ClusterType        string              `json:"cluster_type"`
	User               *User               `json:"user"`
	PlatformKubernetes *PlatformKubernetes `json:"platform_kubernetes"`
	ManagementProject  *ManagementProject  `json:"management_project"`
	Group              *Group              `json:"group"`
}
func (v GroupCluster) String() string {
	return Stringify(v)
}