[NEW] security/py-signedjson: Sign JSON with Ed25519 signatures

python-signedjson allows more than one entity to sign an object, can sign with
more than one key and replace ED25519 with a different algorithm.

WWW: https://github.com/matrix-org/python-signedjson

PR: 205914
Submitted by: Brendan Molloy <brendan+freebsd@bbqsrc.net>