Default AdvancedCacheLoader#publishEntries can hang with more than 2048 entries

The default method for AdvancedCacheLoader#publishEntries relies on the invocation of the process method. This uses the PersistenceManagerCloseableSupplier to handle this. Unfortunately it uses a WithinThreadExecutor, which actually can cause the process method to deadlock with a single thread as it can fill up the queue of 2048 elements.

We should instead use a single threaded executor which would allow the loading of elements and retrieval in parallel on 2 different threads.