Fix Zarr Segmentation Layer json parsing

[fm3]

When parsing the datasource-properties.json, wk previously failed to recognize zarr segmentation layers. They were instead parsed as ZarrDataLayers (discarding segmentation-specific fields like largestSegmentId). The category field was still "segmentation" (creating an invalid state, and leading the frontend to in turn correctly show the layer as a segmentation). The symptom was that you could not create an annotation with this layer as fallback segmentation.

URL of deployed dev instance (used for testing):

• https://fixzarrsegmentationparsing.webknossos.xyz

Steps to test:

• talk to me for a dataset with a zarr segmentation
• load this dataset in your wk, refresh datasets with button in dashboard (as admin) or wait 1min for next scheduled refresh
• create annotation for this dataset (segmentation as fallback is default)
• should work, should be able to brush.

Issues:

• fixes Cannot create annotation with Zarr Segmentation as Fallback Layer #6188

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• Updated (unreleased) changelog
• Needs datastore update after deployment
• Ready for review

[leowe]

LGTM 👍