Expose function resampleKernelImage to python

It would be useful to expose the resampleKernelImage function from https://github.com/Subaru-PFS/drp_stella/blob/master/src/SpectralPsf.cc. This would enable me to use it in my testing and analysis, and to ensure that we are not introducing errors when moving from between analysis of the spots and final implementation in the pipeline.

Additionally, it would be good to better understand the difference between resampleKernelImage function and bin_image function from base LSST code.