Bunch propagation distance is lost when saving bunch to file

[TheresaBruemmer]

When saving the bunch to file, the propagation distance info is lost. This is because wake_t.utilities.bunch_saving.save_bunch_to_file utilises ParticleBunch.get_bunch_matrix, where only the position in the xi plane is saved. So, you do not have any info on position in the beam line when reading bunch from file. I saw that there is get_openpmd_diagnostics_data in ParticleBunch class. Could this be used to save the data when saving to openpmd?