Make GFS CDO directory configurable

• Introduce a MSTRO_ENV_TRANSPORT_GFS_DIR environment variable

• Create a mstro_pc__construct_gfs_path_for_cdo function

  • taking env var into account
  • appending workflow name for isolation
  • possibly creating subdirs by CDO name initial segment to reduce directory size attribute issues

• Use mstro_pc__construct_gfs_path_for_cdo in mstro_pc__handle_initiate_transfer