Add model_version on WorkerActivity

arkindex/process/managers.py

...x/process/migrations/0015_workeractivity_model_version.py

arkindex/process/models.py

arkindex/process/tasks.py

arkindex/process/tests/test_workeractivity.py

arkindex/sql_validation/workeractivity_bulk_insert.sql

...alidation/workeractivity_bulk_insert_no_configuration.sql

...ex/sql_validation/workeractivity_bulk_insert_no_model.sql

...dation/workeractivity_bulk_insert_worker_version_only.sql

arkindex/training/tests/test_model_api.py