Add support for modifying the IAS flavour in creation and modification workflows

gso/workflows/l3_core_service/base_modify_l3_core_service.py

gso/workflows/l3_core_service/ias/create_ias.py

gso/workflows/l3_core_service/ias/create_imported_ias.py

gso/workflows/l3_core_service/ias/modify_ias.py

gso/workflows/l3_core_service/ias/shared.py

...s/l3_core_service/test_create_imported_l3_core_service.py

.../workflows/l3_core_service/test_create_l3_core_service.py

.../workflows/l3_core_service/test_modify_l3_core_service.py