Expose Principled BSDF full customization

[Gerard-Taulats]

Allows to use Blender's internal keywords to access any field inside the Principled BSDF, while preserving current mapped words.

In the YAML file, use the names you'd enter into the "node_bsdf.inputs[...]"
For example to access Transmission field, as per Blender docs the keyword is "Transmission Weight":

layers:
  met1:
    color: [0.63, 0.64, 0.65, 1.0]
    metallic: 0.8
    roughness: 0.3
    Transmission Weight: 0.5