Add JSON schema for zarr datasources

[philippotto]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• edit the settings for a zarr dataset (e.g., add https://data-humerus.webknossos.org/data/zarr/scalable_minds/l4dense_motta_et_al_demo/segmentation via the new ZARR import front-end)
• editing the JSON should work without "invalid JSON" errors

Issues:

• follow-up Add frontend for zarr import #6383

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• Ready for review

[fm3]

Works for me :) I have to say that the error messages are still not particularly readable, but that’s a separate issue I guess.

[philippotto]

I have to say that the error messages are still not particularly readable, but that’s a separate issue I guess.

Yes, that's #5639. Unfortunately, the jsonschema package doesn't really help with readable error messages..
I'd rather put more work into having a form UI so that the user doesn't have to edit the JSON in the first place.