Feature request: Krypton / https://krypt.co/ support for SSH

I'd love support for Krypton (cc @kryptco: @agrinman, @kcking, @ryantberg) - currently Postico (on 1.3.5) errors with the following warning about not supported key type:

even though it's an ssh-rsa key;

```bash
macbooklols:~ russ$ cat ~/.ssh/id_krypton.pub
ssh-rsa AAAAB3NzaC1.......................
```

<3

Start by locating Postico's SSH authentication and key-type handling, then compare it with the Krypton ssh-rsa key described in the issue. No files or tests are named, so identify the relevant entry point and existing SSH coverage first. Done means Krypton keys work for SSH connections without the reported unsupported-key warning.

Written by the indexing model from the issue text.