func (s *ProjectClustersService) DeleteCluster(pid interface{}, cluster int, options ...RequestOptionFunc) (*Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, err
	}
	u := fmt.Sprintf("projects/%s/clusters/%d", pathEscape(project), cluster)
	req, err := s.client.NewRequest(http.MethodDelete, u, nil, options)
	if err != nil {
		return nil, err
	}
	return s.client.Do(req, nil)
}
DeleteCluster deletes an existing project cluster.

GitLab API docs:
https://docs.gitlab.com/ee/api/project_clusters.html#delete-project-cluster
package gitlab
import (
	"fmt"
	"net/http"
	"time"
)
type ProjectClustersService struct {
	client *Client
}
type ProjectCluster 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"`
	Project            *Project            `json:"project"`
}
func (v ProjectCluster) String() string {
	return Stringify(v)
}
type PlatformKubernetes struct {
	APIURL            string `json:"api_url"`
	Token             string `json:"token"`
	CaCert            string `json:"ca_cert"`
	Namespace         string `json:"namespace"`
	AuthorizationType string `json:"authorization_type"`
}
type ManagementProject struct {
	ID                int        `json:"id"`
	Description       string     `json:"description"`
	Name              string     `json:"name"`
	NameWithNamespace string     `json:"name_with_namespace"`
	Path              string     `json:"path"`
	PathWithNamespace string     `json:"path_with_namespace"`
	CreatedAt         *time.Time `json:"created_at"`
}
func (s *ProjectClustersService) ListClusters(pid interface{}, options ...RequestOptionFunc) ([]*ProjectCluster, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/clusters", pathEscape(project))
	req, err := s.client.NewRequest(http.MethodGet, u, nil, options)
	if err != nil {
		return nil, nil, err
	}
	var pcs []*ProjectCluster
	resp, err := s.client.Do(req, &pcs)
	if err != nil {
		return nil, resp, err
	}
	return pcs, resp, err
}
func (s *ProjectClustersService) GetCluster(pid interface{}, cluster int, options ...RequestOptionFunc) (*ProjectCluster, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/clusters/%d", pathEscape(project), cluster)
	req, err := s.client.NewRequest(http.MethodGet, u, nil, options)
	if err != nil {
		return nil, nil, err
	}
	pc := new(ProjectCluster)
	resp, err := s.client.Do(req, &pc)
	if err != nil {
		return nil, resp, err
	}
	return pc, resp, err
}
type AddClusterOptions struct {
	Name                *string                       `url:"name,omitempty" json:"name,omitempty"`
	Domain              *string                       `url:"domain,omitempty" json:"domain,omitempty"`
	Enabled             *bool                         `url:"enabled,omitempty" json:"enabled,omitempty"`
	Managed             *bool                         `url:"managed,omitempty" json:"managed,omitempty"`
	EnvironmentScope    *string                       `url:"environment_scope,omitempty" json:"environment_scope,omitempty"`
	PlatformKubernetes  *AddPlatformKubernetesOptions `url:"platform_kubernetes_attributes,omitempty" json:"platform_kubernetes_attributes,omitempty"`
	ManagementProjectID *string                       `url:"management_project_id,omitempty" json:"management_project_id,omitempty"`
}
type AddPlatformKubernetesOptions struct {
	APIURL            *string `url:"api_url,omitempty" json:"api_url,omitempty"`
	Token             *string `url:"token,omitempty" json:"token,omitempty"`
	CaCert            *string `url:"ca_cert,omitempty" json:"ca_cert,omitempty"`
	Namespace         *string `url:"namespace,omitempty" json:"namespace,omitempty"`
	AuthorizationType *string `url:"authorization_type,omitempty" json:"authorization_type,omitempty"`
}
func (s *ProjectClustersService) AddCluster(pid interface{}, opt *AddClusterOptions, options ...RequestOptionFunc) (*ProjectCluster, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/clusters/user", pathEscape(project))
	req, err := s.client.NewRequest(http.MethodPost, u, opt, options)
	if err != nil {
		return nil, nil, err
	}
	pc := new(ProjectCluster)
	resp, err := s.client.Do(req, pc)
	if err != nil {
		return nil, resp, err
	}
	return pc, resp, err
}
type EditClusterOptions struct {
	Name                *string                        `url:"name,omitempty" json:"name,omitempty"`
	Domain              *string                        `url:"domain,omitempty" json:"domain,omitempty"`
	EnvironmentScope    *string                        `url:"environment_scope,omitempty" json:"environment_scope,omitempty"`
	ManagementProjectID *string                        `url:"management_project_id,omitempty" json:"management_project_id,omitempty"`
	PlatformKubernetes  *EditPlatformKubernetesOptions `url:"platform_kubernetes_attributes,omitempty" json:"platform_kubernetes_attributes,omitempty"`
}
type EditPlatformKubernetesOptions struct {
	APIURL    *string `url:"api_url,omitempty" json:"api_url,omitempty"`
	Token     *string `url:"token,omitempty" json:"token,omitempty"`
	CaCert    *string `url:"ca_cert,omitempty" json:"ca_cert,omitempty"`
	Namespace *string `url:"namespace,omitempty" json:"namespace,omitempty"`
}
func (s *ProjectClustersService) EditCluster(pid interface{}, cluster int, opt *EditClusterOptions, options ...RequestOptionFunc) (*ProjectCluster, *Response, error) {
	project, err := parseID(pid)
	if err != nil {
		return nil, nil, err
	}
	u := fmt.Sprintf("projects/%s/clusters/%d", pathEscape(project), cluster)
	req, err := s.client.NewRequest(http.MethodPut, u, opt, options)
	if err != nil {
		return nil, nil, err
	}
	pc := new(ProjectCluster)
	resp, err := s.client.Do(req, pc)
	if err != nil {
		return nil, resp, err
	}
	return pc, resp, err
}