Automatically close scroll context when returning streamed results

[sothawo]

When using SearchOperations#searchForStream(Query, Class<T>) - and this is used when a repository method is defined to return a Stream<T> - currently it is necessary to call the close() method of the iterator/stream to delete the associated scroll context from Elasticsearch. If this is not done, the scroll context will automatically timeout after 60 seconds, but if many stream are created, then the limit of 500 scroll contexts in Elasticsearch may be reached.

As the implementation knows when all documents are processed, we should call close() automatically when the iterator has no more records so that an explicit closing is not necessary.