Handle application data migration when possible

[freechelmi]

Is your feature request related to a problem? Please describe.
After snap removal and flatpak install the application data is not migrated to the new flatpak

Describe the solution you'd like
Most of the time the application data directory is easy to migrate , we should :

• Save the snap app data somewhere
• purge the snap ( add --purge option )
• install the flatpak
• Copy the app data

Describe alternatives you've considered

Additional context
the data directory of a flatpak is not created before first start , we might need to create it manually , or open and close just once
I would start with thunderbird which is a very common usecase since 24.04

[github-actions]

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