Add reusable two-factor verification for login and money operations (#32)

frontend/packages/sxchnge_analytics/lib/sxchnge_analytics.dart

@@ -2,7 +2,16 @@ import 'dart:async';
 import 'dart:collection';
 import 'dart:math';
 
-enum JourneyKind { login, signup, verification, kyc, topUp, exchange, payout }
+enum JourneyKind {
+  login,
+  signup,
+  verification,
+  kyc,
+  topUp,
+  exchange,
+  payout,
+  security,
+}
 
 enum JourneyStep {
   login,
@@ -18,6 +27,10 @@ enum JourneyStep {
   transferQuote,
   transferSubmission,
   settlement,
+  factorChallenge,
+  factorDelivery,
+  factorVerification,
+  factorSettings,
 }
 
 enum JourneySignal {
@@ -91,6 +104,7 @@ class AnalyticsEvent {
       JourneyKind.topUp => 'top_up',
       JourneyKind.exchange => 'exchange',
       JourneyKind.payout => 'payout',
+      JourneyKind.security => 'security',
       _ => 'auth',
     };
     var stage = step == null ? 'journey' : _snake(step!.name);