Add WorkerVersion.branch

arkindex/documents/fixtures/data.json

arkindex/process/admin.py

arkindex/process/migrations/0043_workerversion_branch.py

arkindex/process/models.py

arkindex/process/serializers/workers.py

arkindex/process/tests/test_corpus_worker_runs.py

arkindex/process/tests/test_user_workerruns.py

arkindex/process/tests/test_workers.py

arkindex/process/tests/worker_runs/test_create.py

arkindex/process/tests/worker_runs/test_list.py

arkindex/process/tests/worker_runs/test_partial_update.py

arkindex/process/tests/worker_runs/test_retrieve.py

arkindex/process/tests/worker_runs/test_update.py

arkindex/sql_validation/indexer_prefetch.sql