U2F as second factor

[raspla]

Is your feature request related to a problem? Please describe.
RocketChat already supports TOTP, which is great, but not as handy as U2F with a hardware token.
Additionally and more important: U2F is more secure and prevents phishing.
Some more details: https://www.yubico.com/blog/otp-vs-u2f-strong-to-stronger/

Multiple vendors support this standard, for example @Nitrokey @solokeys @Yubico @trezor

Describe the solution you'd like
RocketChat should support U2F next to TOTP as second factor.

Additional context
U2F was already mentioned in the original two factor issue RocketChat/Rocket.Chat#1034 (comment)