Get valence from pseudo potential

In DFT+U calculation, user need to specify the manifold for the element, e.g.,

Co: `3d`, O: `2p`

Instead of inputting the value by the user manually, it would be better that we read the valence orbitals from the pseudo-potential and provide a dropdown for the user to select.

@unkcpz, you are the expert on pseudo. Do you know if this is already possible from Aiida? If not, can I assign this to you?

@AndresOrtegaGuerrero, any comments are welcome.