Enhancement: Importing and Exporting

[TimoReusch]

• Resolves: Board export is incomplete for archived cards and card metadata #8041
• Target version: main

Summary

Exporting and importing is kinda unreliable in the current version of deck: not everything on the cards is contained in the export, so replicating a 1:1 copy on a different instance is not possible.

In this PR, we propose a new import / export engine and UI. Users can now select, what should be imported or exported. Its now possible to export and import the entire board as-is including all attachements, archived cards, labels, etc.

Furthermore, by deselecting "Cards" in the import dialog, users can now import only the board structure and use their existing boards as a template for new ones.

New export UI:

New import UI:

I created a small test-board that can be used for validation of the functionality:
Export Validation Board.json

TODO

• Strings are currently in English only. Translations need to be added on Transifex.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Documentation (manuals or wiki) has been updated or is not required