Bump Django 4.2 and DRF 3.15.2

.gitlab-ci.yml

Dockerfile

arkindex/documents/migrations/0003_initial.py

arkindex/documents/serializers/elements.py

arkindex/documents/tests/tasks/test_add_parent_selection.py

arkindex/documents/tests/test_bulk_transcription_entities.py

arkindex/documents/tests/test_destroy_worker_results.py

arkindex/documents/tests/test_entities_api.py

arkindex/documents/tests/test_entity_types.py

arkindex/documents/tests/test_search_api.py

arkindex/documents/tests/test_selection_api.py

arkindex/documents/tests/test_transcriptions.py

arkindex/ponos/tests/test_api.py

arkindex/process/tests/commands/test_cache_worker_runs.py

arkindex/process/tests/test_process_dataset_sets.py

arkindex/process/tests/test_process_elements.py

arkindex/process/tests/test_processes.py

arkindex/process/tests/test_signals.py

arkindex/process/tests/test_workerruns.py

arkindex/process/tests/test_workers.py