Enhance support for multi-tenancy (#1371)

This enhances every ARC controller and the various K8s custom resources so that the user can now configure a custom GitHub API credentials (that is different from the default one configured per the ARC instance).

Ref https://github.com/actions-runner-controller/actions-runner-controller/issues/1067#issuecomment-1043716646

controllers/testresourcereader.go

@@ -0,0 +1,31 @@
+package controllers
+
+import (
+	"context"
+	"errors"
+	"reflect"
+
+	kerrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+type testResourceReader struct {
+	objects map[types.NamespacedName]client.Object
+}
+
+func (r *testResourceReader) Get(_ context.Context, nsName types.NamespacedName, obj client.Object) error {
+	ret, ok := r.objects[nsName]
+	if !ok {
+		return &kerrors.StatusError{ErrStatus: metav1.Status{Reason: metav1.StatusReasonNotFound}}
+	}
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		return errors.New("obj must be a pointer")
+	}
+
+	v.Elem().Set(reflect.ValueOf(ret).Elem())
+
+	return nil
+}