Set a default EventHandler if the provider's main module does not supply one

- Setting a default EventHandler to keep backwards-compatibility
  for the generated providers

Signed-off-by: Alper Rifat Ulucinar <ulucinar@users.noreply.github.com>
(cherry picked from commit 7c2b48d)

Author: ulucinar

pkg/pipeline/templates/setup.go.tmpl

@@ -8,13 +8,19 @@ import (
 	ctrl "sigs.k8s.io/controller-runtime"
 
 	"github.com/upbound/upjet/pkg/controller"
+	"github.com/upbound/upjet/pkg/controller/handler"
 
 	{{ .Imports }}
 )
 
 // Setup{{ .Group }} creates all controllers with the supplied logger and adds them to
 // the supplied manager.
 func Setup{{ .Group }}(mgr ctrl.Manager, o controller.Options) error {
+	// set the default event handler if the provider's main module did not
+	// set one.
+	if o.EventHandler == nil {
+		o.EventHandler = handler.NewEventHandler()
+	}
 	for _, setup := range []func(ctrl.Manager, controller.Options) error{
 		{{- range $alias := .Aliases }}
 		{{ $alias }}Setup,