Allow customizable post-processing parameters and improve results accessibility for phonopy flows

[tomdemeyere]

What would you like to report?

Currently phonopy results are processed through the summarize_phonopy method with fixed, default arguments. Most users will want to specify precise parameters for these calculations, and current post-processing is not ideal since it is only available by opening the saved phonopy files in the quacc directories.

The simplest option seems to include the Phonopy object in the result dictionary one way or another. This would allow users to post-process results at will later on without needing to look into directories. Of course the challenge of this approach is serialization.

A second solution would be to allow the phonon workflow to take additional arguments and pass them to the concerned Phonopy method run_mesh, run_thermal_properties, etc... There is still a problem for users who would like to run other, specific/expert methods, not present in the summarize_phonopy.