Set `bfgs_trad` as `bfgs` and other suggestions for `relax_method`

[QuantumMisaka]

Describe the Code Quality Issue

bfgs_trad as the newest BFGS method (algorithm like which in ASE) has been widely used in user community and get good response, while old bfgs method (algorithm like which in QE) tend to have problem and can be replaced. However, the old bfgs method tend to be used in prefer for fresh users due to its simplicity, and user my think this bfgs is a more recommended method. So I consider that we can use bfgs as a representation of the bfgs_trad method, while the old bfgs can be changed to another longer name.

Additional Context

Also, the default value of relax_method is cg, which is normal but the efficiency tend to be lower than the BFGS in ASE (as 'bfgs_trad' in ABACUS now), I think we can also change the default value of relax_method.

[dyzheng]

Good suggestion, I will modify it.

[mohanchen]

That's a good idea.