support Ed25519 keys

[cburroughs]

As of this writing Triton does not have server side support for Ed25519 keys and on first glance BouncyCastle does not support them either. However, we would eventually support them.

[cburroughs]

So Apache Mina SSHD supports Ed25519 by way of https://github.com/str4d/ed25519-java. I had initially dismissed this library on the fear that "pure java" == slow, and the vigorous disclaimer in the READEMD. FWIW This is library is also used by gerrit.

[bahamat]

Currently ed25519 keys aren't supported by x509, which is partly why it's not supported in Triton yet.

https://datatracker.ietf.org/doc/draft-ietf-curdle-pkix/