Magnification parameter

### Description of feature

Hey @JLrumberger ,

I just wanted to ask why the `--magnification` parameter in the `MultiplexDataset` is hardcoded to 20 and is not showing up in the tutorial? Shouldn't that be a highly important parameter to set depending on which microscope/platform the image was acquired on (e.g. CODEX has a much higher resolution thatn IMC etc.). If the dataset has a MPP of 1, does it make sense to set magnification to 10? Did I trace that correctly?

Thanks!