Feature Request: Support cache.SharedIndexInformer for auto-triggering

[Dentrax]

As we already discussed this idea in Slack, dropping here so we do not forget!

---

Instead of run operator as scheduled runs using CronJob, we can use NewSharedIndexInformer to create an event loop in order to detect image changes instantly. For example;

deploymentInformer := cache.NewSharedIndexInformer(
			&cache.ListWatch{
				ListFunc: func(options metaV1.ListOptions) (runtime.Object, error) {
					return clientSet.AppsV1().Deployments(metaV1.NamespaceAll).List(ctx, options)
				},
				WatchFunc: func(options metaV1.ListOptions) (watch.Interface, error) {
					return clientSet.AppsV1().Deployments(metaV1.NamespaceAll).Watch(ctx, options)
				},
			},
			&appsV1.Deployment{},
			0,
			cache.Indexers{},
		)

Eventually we are able to get all add/update/remove events:

informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc: func(obj interface{}) {
			//
		},
		UpdateFunc: func(old, new interface{}) {
			//
		},
		DeleteFunc: func(obj interface{}) {
			//
		},
	})

P.S: We also do not want to drop scheduled runs. But both features are actually mutually-exclusive. So one of run type must be chosen in the config.

cc @developer-guy