Commits on Jun 2, 2022

1. feat(recipe): add ExistingDataWatch class …

   This adds a subclass of DataWatch which only operates on existing
   ZNodes.  If a user uses a DataWatch on a path and the ZNode at that
   path is deleted, the DataWatch will still issue an "exists" call
   and set a watch right before the final callback.  That means that
   regardless of the return value of the callback and whether or not
   Kazoo will invoke the callback again, the ZooKeeper server still
   has a watch entry for that path.
   
   In short, using a DataWatch on a path and then deleting that path
   can leak watch entries on the ZooKeeper server.
   
   Because the DataWatch recipe is designed to watch non-existing paths,
   this behavior may be desired and relied on by some users, so it's
   not considered a bug.  But other users may want to use DataWatches
   for nodes where this behavior would be a problem.
   
   The ExistingDataWatch class behaves similarly to its parent class,
   DataWatch, but it does not set a watch on paths which do not exist
   (whether that's because they never existed or were recently deleted).
   This means that a user of an ExistingDataWatch can be assured that
   after the callback with the deleted event, the watch is removed from
   the server.

   

   jeblair authored and ceache committed Jun 2, 2022
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