The Resource[T] provides access to a Kubernetes resource as an
observable stream of events or as via a read-only Store[T]:

   type Resource[T k8sRuntime.Object] interface {
   	stream.Observable[Event[T]]
   	Store(context.Context) (Store[T], error)
   }

An event is either *SyncEvent, *UpdateEvent or *DeleteEvent. The
event can be processed synchronously with event.Handle(onSync,
onUpdate, onDelete), or asynchronously with a type switch and call
to event.Done(err). On non-nil errors from event handling the key
corresponding to the object being handled is requeued for later
processing and after retries are exhausted the stream completes with
the error from final retry.

The Store() method blocks until the resource has been synchronized with
the api-server (e.g. CachesSynced == true).  Store[T] is a wrapper around
cache.Store that only provides the methods that are safe to use (Get,
GetByKey, List, ListKeys) and that are specialized to type T.

This abstracts the management of an informer and cache behind the
`NewResourceConstructor` function that takes a cache.ListerWatcher
and provides a constructor that can be used from a cell to provide the
Resource to the application:

   var exampleCell = hive.NewCell(
           "example",
           fx.Provide(
                   // Provide `Resource[*slim_corev1.Pod]` to the application:
                   resource.NewResourceConstructor(func(c k8sClient.Clientset) cache.ListerWatcher {
                           return utils.ListerWatcherFromTyped[*slim_corev1.PodList](c.Slim().CoreV1().Pods(""))
                   }),
           }),
           ...
   )

Resource is implemented as an informer whose handlers enqueue the
changes keys to per-subscriber queues, from which a key is dequeued,
the objects then retrieved from the cache.Store and then provided
to the subscriber. This allows subscribers to process the changes
at their own pace and allows coalescing changes to the same key when
the subscriber is slow.

Signed-off-by: Jussi Maki <jussi@isovalent.com>

Example for how Resource[T] can be used in a complete application.

Signed-off-by: Jussi Maki <jussi@isovalent.com>