[Extensions] Introduce ClientBehaviour model

[msirringhaus]

Extension processing also alter platform behaviour. As an example 12.1. Credential Protection (credProtect) may require performing additional authenticator checks, in certain circumstances. The need for these checks may be represented in a new ClientBehaviour struct, to be potentially altered during extension processing:

    trait ClientExtensionProcessing<G, C> {
      fun get(&self, input: &G, &mut clientBehaviour: ClientBehaviour): ExtensionResult<CborMap>
      fun create(&self, input: &C, &mut clientBehaviour: ClientBehaviour): ExtensionResult<CborMap>
    }

Originally posted by @AlfioEmanueleFresta in #77 (comment)