add migration tools

One of the primary benefits of the ATproto is the ability to migrate data hosts baked into the protocol. With the advent of web-based services like tektite, PDSMoover, and ATP Airport the process has become much easier to migrate accounts between PDS servers.

Migration services/tools

• tektite: https://github.com/blacksky-algorithms/tektite-cc-migration-service
• pdsmoover: https://tangled.org/@baileytownsend.dev/pds-moover
• ATP Airport: https://tangled.org/@knotbin.com/airport
• goat cli tool (already in nixpkgs): https://github.com/bluesky-social/goat/

Backup services/tools

• atbackup (tauri based GUI): https://tangled.org/@atbackup.pages.dev/atbackup