Add information to "Migration" screen

[MoritzKa]

Currently the Migration screen in Alby Hub does not provide important information:

1. The migration is not available if VSS is enabled.
2. The migration is not possible from an LDK-based Alby Hub to LND-based Umbrel or Start9 nodes.

We could link to this guide or add both limitations to the warning box on the screen.

[rolznz]

@MoritzKa

The migration is not available if VSS is enabled.

This should work fine. However, they will need a paid DIY plan within a few months to ensure they continue to have VSS access.

[rolznz]

@MoritzKa for point 2, I think this solves it and other similar issues:

Migration Requires a Fresh Alby Hub

To import the migration file, you must have a brand new Alby Hub on another device and use the "Advanced" option in the onboarding.