cmd/k8s-operator,k8s-operator,go.mod: optionally create ServiceMonitor (#14248)

* cmd/k8s-operator,k8s-operator,go.mod: optionally create ServiceMonitor

Adds a new spec.metrics.serviceMonitor field to ProxyClass.
If that's set to true (and metrics are enabled), the operator
will create a Prometheus ServiceMonitor for each proxy to which
the ProxyClass applies.
Additionally, create a metrics Service for each proxy that has
metrics enabled.

Updates tailscale/tailscale#11292

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

k8s-operator/apis/v1alpha1/register.go

@@ -10,6 +10,7 @@ import (
 
 	"tailscale.com/k8s-operator/apis"
 
+	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -39,12 +40,18 @@ func init() {
 	localSchemeBuilder.Register(addKnownTypes)
 
 	GlobalScheme = runtime.NewScheme()
+	// Add core types
 	if err := scheme.AddToScheme(GlobalScheme); err != nil {
 		panic(fmt.Sprintf("failed to add k8s.io scheme: %s", err))
 	}
+	// Add tailscale.com types
 	if err := AddToScheme(GlobalScheme); err != nil {
 		panic(fmt.Sprintf("failed to add tailscale.com scheme: %s", err))
 	}
+	// Add apiextensions types (CustomResourceDefinitions/CustomResourceDefinitionLists)
+	if err := apiextensionsv1.AddToScheme(GlobalScheme); err != nil {
+		panic(fmt.Sprintf("failed to add apiextensions.k8s.io scheme: %s", err))
+	}
 }
 
 // Adds the list of known types to api.Scheme.