Use a batch (default size of 50) publication in all bulk endpoint helpers

arkindex_worker/image.py

arkindex_worker/utils.py

arkindex_worker/worker/__init__.py

arkindex_worker/worker/classification.py

arkindex_worker/worker/element.py

arkindex_worker/worker/entity.py

arkindex_worker/worker/metadata.py

arkindex_worker/worker/transcription.py

tests/test_elements_worker/test_classifications.py

tests/test_elements_worker/test_elements.py

tests/test_elements_worker/test_entities.py

tests/test_elements_worker/test_metadata.py

tests/test_elements_worker/test_transcriptions.py

tests/test_utils.py