Add support for FIDO2-backed SSH keys

Summary:
U2F/FIDO are open standards for inexpensive two-factor authentication hardware that are widely used for website authentication.

These keys are available since OpenSSH 8.2 (2020-02-14).

https://www.openssh.com/txt/release-8.2

https://security.stackexchange.com/q/240991/260234

Ref Q96

Test Plan: Check the added keys. They exactly match the output of the command 'ssh -Q key'.

Reviewers: O1 Blessed Committers, antonia, avivey

Reviewed By: O1 Blessed Committers, antonia, avivey

Subscribers: avivey, tobiaswiese, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25508