Support ECDSA SSH keys and FIDO/U2F key types in Lagoon

[smlx]

The YubiKey 5 Series supports the following algorithms on the PIV smart card application.

RSA 1024
RSA 2048
ECC P-256
ECC P-384

https://support.yubico.com/support/solutions/articles/15000014219-yubikey-5-series-technical-manual

I'd like to use my Yubikey to interact with Lagoon via SSH, but only RSA and Ed25519 keys are supported by Lagoon. For various reasons RSA 2048-bit keys aren't great so it would be nice to add support for at least ecdsa-sha2-nistp256, and possibly ecdsa-sha2-nistp384.

[smlx]

Lagoon should also support the FIDO/U2F key types ecdsa-sk and ed25519-sk.
https://www.openssh.com/txt/release-8.2

[tobybellwood]

As long as the key type is parsable by sshpk - it should be easyish to add in.

I'm not sure that the *-sk are supported by sshpk, so we may need to look to validate somehow else?

[smlx]

Looks like it isn't supported TritonDataCenter/node-sshpk#72

[smlx]

Even the non sk versions will make it easier to use Yubikeys.

[tobybellwood]

ECDSA key support is now in Lagoon

[tobybellwood]

Going to reopen this to track the -sk key types