Implement AuthenticationMethod WIFI security

Currently only open AP is implemented. It is convenient and "enough" for many cases provided that SSH key material is secure, but it'd be nice to have that extra layer of security.

[See esp-radio's AuthenticationMethod enum for a list of supported mechanisms](https://github.com/esp-rs/esp-hal/blob/6168bc775349ba35e3c27bb527defccb22a44658/esp-radio/src/wifi/mod.rs#L85)