Document FIDO2 support in ./lib/auth/webauthncli (#11955)
Document FIDO2 support in ./lib/auth/webauthncli (#11955)

Document the different implementations, fallbacks, build tags, and provide some
install/use instructions.

#9160

* Document FIDO2 support in ./lib/auth/webauthncli
* Add license
gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport