Add an exisiting zarr array as a mag to a dataset

[normanrz]

Detailed Description

• Affected library: e.g. webknossos

Add a function to the Layer to add an existing Zarr as a mag. Probably that would need a move of the Zarr array.

A followup could be to add a function to the Dataset to add an OME-Zarr image by examining the metadata and adding the mags automatically.

Use Cases & Context

Users that have existing Zarr data would like to upload it to Webknossos. For that, the most straight-forward way is to assemble a Dataset and then use the upload method.