Add layer + mag dir to wkw uploads if missing

[fm3]

When a user uploads wkw-converted data directly, that is not in a layer directory or not even in a mag directory, the back-end now automatically adds those to the path.

A risk to this method is that layers called 1, 1-1-1 or z0 etc would be mistaken for mags/bucket paths and this would trigger wrongly. But I’ll assume this will rarely be the case.

URL of deployed dev instance (used for testing):

• https://uploadwkwdir.webknossos.xyz

Steps to test:

• upload only parts of the dataset
• should be moved (console logging), and viewable after import

Issues:

• fixes Dataset upload: add default layer name and mag if not present #5219

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

[youri-k]

LGTM

While testing, I stumbled across this typo: https://github.com/scalableminds/webknossos/blob/upload-wkw-dir/frontend/javascripts/admin/dataset/dataset_add_view.js#L99
Would you mind including a fix for this?