Fix Kotlin DSL webAuthn { }

[franticticktick]

WebAuthnDsl is implemented incorrectly, we need to change the implementation of the get() method according to the usual spring security template, as in other kotlin DSLs. Now, due to incorrect implementation, the default configuration will not work.

        @Bean
        open fun securityFilterChain(http: HttpSecurity): SecurityFilterChain {
            http{
                formLogin { }
                webAuthn { }
            }
            return http.build()
        }

In addition, the DSL is missing disableDefaultRegistrationPage.