Add support for Visium CytAssist image

[ZheFrench]

Sometime you can have an extra image cytassist_image.tiff if you use Cytassist to transfer transcriptomic probes from standard glass slides to Visium slides.

I think the scale factor related to this image is regist_target_img_scalef.

scalefactors_json.json {"regist_target_img_scalef": 0.17107664, "tissue_hires_scalef": 0.057025548, "tissue_lowres_scalef": 0.017107664, "fiducial_diameter_fullres": 322.2879096308676, "spot_diameter_fullres": 214.85861109947552}

You do a grep and filter based on accepted list of keyword to find the good image and associate scalefactor.

Could be upgraded to add support for this Cytassist image which I stil don't know is considered for the full res image or not but that is another consideration.