Enable Zarr download

### Background
How should we handle direct downloads moving forward?...amongst other things!

Previously when preparing a CFE dataset, we needed to separately prepare images for 3d visualization, 2D hover thumbnail, and a downloadable version. Downloadable versions have to be placed in a very specific download server that works with a server app that is currently unmaintained.

"old CFE":
* one OME.TIFF file created by merging an original microscopy CZI file with a segmentation TIFF file (for direct download)
* one PNG thumbnail
* one "texture atlas" for 3d viewer, which is really one json file plus 3 associated PNG files. This has been downsampled from the original for fast visualization.

"new CFE"
* one PNG thumbnail
* one OME-Zarr which contains both the full resolution image channels (merged from original CZI and TIFF segmentation) plus downsampled channels suitable for fast visualization

Preparing the images is very time consuming and also redundant when the 3d visualizable file could use the same storage. Also, there is a problem when the "file" is not a single file at all but a collection such as Zarr. The direct download server does not quite support this use case. OME-Zarr data is intended to REMAIN in the cloud, and be accessed from there rather than downloaded all at once in bulk.

### User needs statement(s)
As a scientist, I need direct access to the images presented in Cell Feature Explorer for further research after my CFE user session is over.

### Size
Lg

### Requirements
This touches on questions like how and where do we release image data? Can we do it without having to store it redundantly? Can we do it without having to recombine multiple images into one (such as merging a raw microscope image with it segmented image)?
Can we make sure CFE fully hides all download buttons when downloadable data is not provided?
Can CFE offer an alternative to a direct download by instead providing a URL to the data location?

### Deliverables
A plan for CFE downloads that covers all possible user flows.

### Stakeholder(s)
@toloudis @gj210 @meganrm

### Timeline

### Notes