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_test.go

@@ -0,0 +1,35 @@
+package controllers
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+func TestResourceReader(t *testing.T) {
+	rr := &testResourceReader{
+		objects: map[types.NamespacedName]client.Object{
+			{Namespace: "default", Name: "sec1"}: &corev1.Secret{
+				ObjectMeta: metav1.ObjectMeta{
+					Namespace: "default",
+					Name:      "sec1",
+				},
+				Data: map[string][]byte{
+					"foo": []byte("bar"),
+				},
+			},
+		},
+	}
+
+	var sec corev1.Secret
+
+	err := rr.Get(context.Background(), types.NamespacedName{Namespace: "default", Name: "sec1"}, &sec)
+	require.NoError(t, err)
+
+	require.Equal(t, []byte("bar"), sec.Data["foo"])
+}