separate initial load to avoid retaining list items in memory

[rafaelri]

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Local variables list and items will retain the list of objects returned in the initial list in the heap while the Thread that is running run is alive. Leading to a minor but still a leak since those objects could be collected if the local variable was made out of scope. This PR separates the initial load in a separate method that returns the resourceVersion and shortens the scope of the variables mentioned to allow garbage collection.

 ApiListType list =
          listerWatcher.list(
              new CallGeneratorParams(Boolean.FALSE, getRelistResourceVersion(), null));

      V1ListMeta listMeta = list.getMetadata();
      String resourceVersion = listMeta.getResourceVersion();
      List<? extends KubernetesObject> items = list.getItems();

This PR also removes the watcher attribute and replaces the closing logic to release resources as soon as the events on a particular watcher have been processed.