Fix Getting Kubeclient in OpenShift Extension of Pipeline

There is an issue introduced in PR: tektoncd#1530 (https://github.com/tektoncd/operator/pull/1530/files#diff-7f51fd839c96e48ad11d43ad6e8e502cccfb00405087d1c8e116fc6245fad615R92)

```
panic: Unable to fetch k8s.io/client-go/kubernetes.Interface from context. This context is not the application context (which is typically given to constructors via sharedmain).

goroutine 2705 [running]:
go.uber.org/zap/zapcore.CheckWriteAction.OnWrite(0x0?, 0x1e4bde2?, {0x0?, 0x0?, 0xc0023ea000?})
        /go/src/github.com/tektoncd/operator/vendor/go.uber.org/zap/zapcore/entry.go:198 +0x65
go.uber.org/zap/zapcore.(*CheckedEntry).Write(0xc000335ad0, {0x0, 0x0, 0x0})
        /go/src/github.com/tektoncd/operator/vendor/go.uber.org/zap/zapcore/entry.go:264 +0x3ec
go.uber.org/zap.(*SugaredLogger).log(0xc001166940, 0x4, {0x0?, 0x1ac1701?}, {0xc000e25450?, 0x40dc07?, 0x3497c2e1ffdc0d75?}, {0x0, 0x0, 0x0})
        /go/src/github.com/tektoncd/operator/vendor/go.uber.org/zap/sugar.go:295 +0xee
go.uber.org/zap.(*SugaredLogger).Panic(...)
        /go/src/github.com/tektoncd/operator/vendor/go.uber.org/zap/sugar.go:153
knative.dev/pkg/client/injection/kube/client.Get({0x2149358, 0xc0017f2bd0})
        /go/src/github.com/tektoncd/operator/vendor/knative.dev/pkg/client/injection/kube/client/client.go:201 +0x1b7
github.com/tektoncd/operator/pkg/reconciler/openshift/tektonpipeline.openshiftExtension.PreReconcile({0xc0007d4320?}, {0x2149358, 0xc0017f2bd0}, {0x2163a08?, 0xc000d89180?})
        /go/src/github.com/tektoncd/operator/pkg/reconciler/openshift/tektonpipeline/extension.go:92 +0x426
github.com/tektoncd/operator/pkg/reconciler/kubernetes/tektonpipeline.(*Reconciler).ReconcileKind(0xc0009a1100, {0x2149358, 0xc0017f2bd0}, 0xc000d89180)
        /go/src/github.com/tektoncd/operator/pkg/reconciler/kubernetes/tektonpipeline/reconcile.go:87 +0x687
github.com/tektoncd/operator/pkg/client/injection/reconciler/operator/v1alpha1/tektonpipeline.(*reconcilerImpl).Reconcile(0xc000410280, {0x2149358, 0xc0017f2ba0}, {0xc00188d1f8, 0x8})
        /go/src/github.com/tektoncd/operator/pkg/client/injection/reconciler/operator/v1alpha1/tektonpipeline/reconciler.go:236 +0x582
knative.dev/pkg/controller.(*Impl).processNextWorkItem(0xc0008ed1a0)
        /go/src/github.com/tektoncd/operator/vendor/knative.dev/pkg/controller/controller.go:542 +0x58d
knative.dev/pkg/controller.(*Impl).RunContext.func3()
        /go/src/github.com/tektoncd/operator/vendor/knative.dev/pkg/controller/controller.go:491 +0x68
created by knative.dev/pkg/controller.(*Impl).RunContext
        /go/src/github.com/tektoncd/operator/vendor/knative.dev/pkg/controller/controller.go:489 +0x312

```

pkg/reconciler/openshift/tektonpipeline/extension.go

@@ -28,6 +28,7 @@ import (
 	"github.com/tektoncd/operator/pkg/reconciler/common"
 	"github.com/tektoncd/operator/pkg/reconciler/kubernetes/tektoninstallerset/client"
 	occommon "github.com/tektoncd/operator/pkg/reconciler/openshift/common"
+	"k8s.io/client-go/kubernetes"
 	kubeclient "knative.dev/pkg/client/injection/kube/client"
 	"knative.dev/pkg/logging"
 )
@@ -50,12 +51,14 @@ func OpenShiftExtension(ctx context.Context) common.Extension {
 		// value through extension not going to affect execution
 		installerSetClient: client.NewInstallerSetClient(operatorclient.Get(ctx).OperatorV1alpha1().TektonInstallerSets(),
 			version, "pipelines-ext", v1alpha1.KindTektonPipeline, nil),
+		kubeClientSet: kubeclient.Get(ctx),
 	}
 	return ext
 }
 
 type openshiftExtension struct {
 	installerSetClient *client.InstallerSetClient
+	kubeClientSet      kubernetes.Interface
 }
 
 func (oe openshiftExtension) Transformers(comp v1alpha1.TektonComponent) []mf.Transformer {
@@ -89,8 +92,7 @@ func (oe openshiftExtension) PreReconcile(ctx context.Context, comp v1alpha1.Tek
 	}
 
 	// reconcile namespace with updated labels
-	kubeClientSet := kubeclient.Get(ctx)
-	return common.ReconcileTargetNamespace(ctx, labels, comp, kubeClientSet)
+	return common.ReconcileTargetNamespace(ctx, labels, comp, oe.kubeClientSet)
 }
 
 func (oe openshiftExtension) PostReconcile(ctx context.Context, comp v1alpha1.TektonComponent) error {