FEP-2a62: signed account migration

Heya, this is a discussion for FEP-2a62.

This FEP is an attempt at specifying a hopefully stable migration process for accounts between different servers. The process is inspired by polyproto’s migration specification.

TLDR: Old server collects all events and objects of the migrating user, signs each individually with user’s private key and exports as archive. New server verifies signatures, then re-sends all events and objects in chronological order, attaching a link to the old id and the signature of that id, as generated by the old server.

Feedback would be very much appreciated