Export / Import of Shelves

[kaipee]

Is your feature request related to a problem? Please describe.
No real problem, just a request.

Describe the solution you'd like
I have moved from self installed calibre-web to containerized calibre-web. The version I moved from is quite old so I haven't just copied across my app.db - I just manually re-created users and re-applied the same settings.

Only thing missing is all of the shelves that were previously created. Is there an easy way to pull these (and book id matches) from the db somewhere? It would be good to have an export/import feature for them.

Describe alternatives you've considered
Unsure there are any?