Avoid schema definition duplication in settings

[fcollonval]

With the introduction of menus and toolbars customization through settings, the schema definition tends to be duplicated in multiple extensions

=> I wonder if we could publish our own types under some URL to avoid repeating this. It might make updating to new versions easier as well.

Originally posted by @krassowski in #10469 (comment)

@fcollonval

Indeed this would be nice. The true source should probably the settings schema. Do you know how and where to publish such schema ?

@krassowski

One option would be https://www.schemastore.org/json/ (I think they would accept one or two shema files for JupyterLab but we should not be publishing too many files there). Another potential option would be to publish it on jupyter.org which might be more reliable long-term but would need a few people to agree (and more work). For proof-of-concept I would start by linking to one of the settings schema on GitHub (via raw.githubusercontent.com or similar to get the raw file) and see if the references work.

Edit: I never did it before, but I believe it is technically possible. I may be wrong though.