whether or not that one can skip 'cell_type' setting in dpgen init_bulk

[Sanwen-Yang]

D

[kaiqi-wang]

I think it is feasible. The cell_type parameter in dpgen init_bulk only support five choices, ie, fcc, bcc, hcp, sc and diamond. It is obvious it can not contain all possible cell type. So POSCAR and STRU format are support in dpgen to read specical structure. We can directly use the from_poscar and from_poscar_path parameters to identify cell_type atuomatically.