Support encypted Ed25519 SSH keys

Unencrypted (no passphrase) Ed25519 SSH keys work fine, but when using an encrypted (with a passphrase) Ed25519 SSH key, the following currently happens...

```sh
...
SSH Key Passphrase [none]: •••••
error adding private key: error parsing private key: ssh: cannot decode encrypted private keys
...
$ > 
```