FEP-7628: Move actor
https://codeberg.org/fediverse/fep/src/branch/main/fep/7628/fep-7628.md
This #FEP is an attempt to make a synthesis of various approaches to implementing portable identities on Fediverse: Mastodon's "Move to a different account" feature, Nomadic Identity in Hubzilla and Streams, and FEP-c390 identity proofs.