git example unikernel: abstract using rsa and ed25519 keys

[Hannes Mehnert]

At the moment, this is hardcoded to rsa in mimic. It would be nice to have a boot flag whether a rsa or a ed25519 key is to be used. Eventually it makes sense to rethink the key seed & keytype argument into a single "ed25519:" / "rsa:"... same for the authenticator (which is the ssh fingerprint but does not include the key type (there's Awa.Keys.authenticator_of_string which includes the type)).

Maybe Awa should provide a sensible interface first how to deserialise a ssh key (from seed / direct), similar to authenticator?

[Calascibetta Romain]

This issue is closed by the Awa.Keys.of_string