Compile flag for AuthenticatorConfig (#628)

* Adds a compile flag for AuthenticatorConfig

The command can be disabled for authenticators that don't want users to
change their configuration.

* adds tool for calling Config

* std now implies config_command

* removes obsolete comment

libraries/opensk/src/ctap/client_pin.rs

@@ -119,6 +119,7 @@ pub enum PinPermission {
     CredentialManagement = 0x04,
     _BioEnrollment = 0x08,
     LargeBlobWrite = 0x10,
+    #[cfg(feature = "config_command")]
     AuthenticatorConfiguration = 0x20,
 }