Zarr backend followup: OME-NGFF, user-side improvements

[fm3]

Follow-up for reading zarr images in wk-backend backend (https://github.com/scalableminds/webknossos/pull/6019)

• [x] handle multi-layers/ngff
  • [x] handle OME-NGFF metadata https://github.com/scalableminds/webknossos/pull/6335
  • [x] handle non-standard axis order (as specified by ome metadata?) https://github.com/scalableminds/webknossos/pull/6335
• [ ] pass through channels all the way to the front-end
• [ ] expose as first-class feature to users
  • [ ] adapt frontend compatibility detection for upload
  • [x] routes to add remote datasets https://github.com/scalableminds/webknossos/pull/6335
  • [ ] adapt documentation
  • [ ] Store Credentials on wk side in db rather than in datasource-properties.json
  • [ ] Do remote datasets need a datasource-properties.json at all?