Support chunking semantically distinct frames into separate files

[aliddell]

What we need

We would like to be able to dispatch interleaved channel frames into different chunks. For example, it is sometimes the case that a single frame represents a channel, so that frames come in in order, e.g., R, G, B, R, G, B, R, ...
We would like to be able to send each frame to a separate chunk.

Why we need it

This will aid compression and analysis.

Definition of done

• A user can specify a frame chunking scheme via the storage settings.
• An acquisition to a Zarr dataset should be chunked accordingly.