Support 2D yx data in Cellpose task

[jluethi]

Currently, the Cellpose task only supports 2D data when it's saved as czyx, cyx or zyx (e.g. 1, 2560, 2160). See original discussion here: #398

Not supporting yx data from faim-ipa has become somewhat of a blocker. The clean solution to this will come with ngio. I'll explore options to enable this in a hackier way beforehand to enable some user workflows.