Move training worker run creation from build_workflow to training process serializer

.../migrations/0017_remove_process_model_version_and_more.py

arkindex/process/models.py

arkindex/process/serializers/training.py

arkindex/process/tests/test_create_training_process.py

arkindex/sql_validation/process_elements_filter_ml_class.sql

arkindex/sql_validation/process_elements_filter_type.sql

arkindex/sql_validation/process_elements_top_level.sql

arkindex/sql_validation/process_elements_with_image.sql

arkindex/training/tests/test_model_api.py