Build tours in Advanced Settings/overrides.json?

[bollwyvl]

A common thing I end up wanting is a specific tour for just one repo deployed on binder, as part of a constructor build, or soon, https://github.com/jtpio/jupyterlite/issues/31.

From a binder/lite perspective, it seems like being able to use the declarative schema in overrides.json might be the lowest-touch way to get something out the door for an end user. This would be a natural place to get at least initial support for schema validation, even though there's no autocomplete, etc.

Additionally, if I know my audience already knows JupyterLab, having a "big hammer" "dont-show-any-damned-toasts": true might be handy, both at the per-tour level, as well as a global setting.

I haven't poked around the codebase in a while, maybe I'll freshen up and see if i can get a PR together...