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

[ulucinar]

Description of your changes

While updating the upjet dependency to the main HEAD, @haarchri figured out that the recently introduced changes with #231 are not backwards-compatible. This PR makes those changes backwards-compatible by setting a default event handler if one is not already set by the provider's main module. The provider may set the event handler with something like:

o := tjcontroller.Options{
		Options: xpcontroller.Options{
			Logger:                  log,
			GlobalRateLimiter:       ratelimiter.NewGlobal(*maxReconcileRate),
			PollInterval:            *pollInterval,
			MaxConcurrentReconciles: *maxReconcileRate,
			Features:                &feature.Flags{},
		},
		Provider:       config.GetProvider(),
		SetupFn:        clients.TerraformSetupBuilder(*terraformVersion, *nativeProviderSource, *providerVersion),
		WorkspaceStore: terraform.NewWorkspaceStore(log, terraform.WithDisableInit(len(*nativeProviderPath) != 0), terraform.WithProcessReportInterval(*pollInterval), terraform.WithFeatures(featureFlags)),
		EventHandler: handler.NewEventHandler(),
	}

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Tested against crossplane-contrib/provider-pagerduty.

[haarchri]

its working

can also see the following change in generated files:

 func Setup(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()
+       }