OpenPubKey support

**Is your feature request related to a problem? Please describe.**
There is appearently a way to use OIDC to sign packages and [even ssh into servers](https://blog.cloudflare.com/open-sourcing-openpubkey-ssh-opkssh-integrating-single-sign-on-with-ssh/) called [OpenPubKey](https://github.com/openpubkey/openpubkey), this can connect identities and public keys, improving access control

**Describe the solution you'd like**
I would love to be able to bind public keys to existing identities in authentik