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.
This enhances the existing time.Duration parser to allow multiple units, and implements a decode hook which can be used by koanf to decode string/integers into time.Durations as applicable.
This change addresses an issue with the usage of the full sender configuration option in the MAIL FROM SMTP command. If a user includes a name in the sender this shouldn't be sent in the MAIL FROM command, instead we should extract it and use just the email portion.
Fixes#2571
