This implements Webauthn. Old devices can be used to authenticate via the appid compatibility layer which should be automatic. New devices will be registered via Webauthn, and devices which do not support FIDO2 will no longer be able to be registered. At this time it does not fully support multiple devices (backend does, frontend doesn't allow registration of additional devices). Does not support passwordless.
Adds encryption to the U2F public keys. While the public keys cannot be used to authenticate, only to validate someone is authenticated, if a rogue operator changed these in the database they may be able to bypass 2FA. This prevents that.
This adds an AES-GCM 256bit encryption layer for storage for sensitive items. This is only TOTP secrets for the time being but this may be expanded later. This will require a configuration change as per https://www.authelia.com/docs/configuration/migration.html#4330.
Closes#682
