Generate valid structure for MakeCredential params

* Add crate arbitrary as ctap's optional dependency, when feature "fuzz"
  is activated.

* Derive Arbitrary for all the necessary types in order to generate the
  concrete types from random bytes.

* Add a fuzz target that transforms the input to valid format for
  MakeCredential.

libraries/cbor/src/values.rs

@@ -225,6 +225,12 @@ impl From<&str> for Value {
     }
 }
 
+impl From<Vec<Value>> for Value {
+    fn from(array: Vec<Value>) -> Self {
+        Value::Array(array)
+    }
+}
+
 impl From<Vec<(Value, Value)>> for Value {
     fn from(map: Vec<(Value, Value)>) -> Self {
         Value::Map(map)