Create endpoint to generate presigned URLs for any Zarr chunk

[kabilar]

This feature request is to allow viewing embargoed Zarrs in NeuroGlass.

From an email thread:

... a new DANDI API service that generates a presigned URL for any chunk of a Zarr archive, is that right? This would be analogous to the already existing ability for our API to create presigned URLs for non-Zarr assets, which is much simpler because those assets are identified one-to-one with a single file (unlike Zarrs).

[kabilar]

Assigning Jake since Roni mentioned that Jake is currently working on the design.

[jjnesbitt]

We've had discussions on this topic. While blindly generating pre-signed URLs for any zarr chunk request made to the API is one possible approach, it would very quickly suffer from scale, since pre-signing is a computationally intensive operation (compared to handling a normal request).

We've got some thoughts on how we can approach this is a more performant way, which we'll be investigating soon.