Auth/PM-6198 - Registration with Email Verification - Add email clicked endpoint (#4520)

* PM-6198 - RegistrationEmailVerificationTokenable - add new static validate token method

* PM-6198 - Rename RegistrationStart to Registration as we now have to add another anonymous reference event.

* PM-6198 - rest of work

* PM-6198 - Unit test new account controller method.

* PM-6198 - Integration test new account controller endpoint

src/Core/Tools/Enums/ReferenceEventSource.cs

@@ -10,6 +10,6 @@ public enum ReferenceEventSource
     User,
     [EnumMember(Value = "provider")]
     Provider,
-    [EnumMember(Value = "registrationStart")]
-    RegistrationStart,
+    [EnumMember(Value = "registration")]
+    Registration,
 }

src/Core/Tools/Enums/ReferenceEventType.cs

@@ -6,6 +6,8 @@ public enum ReferenceEventType
 {
     [EnumMember(Value = "signup-email-submit")]
     SignupEmailSubmit,
+    [EnumMember(Value = "signup-email-clicked")]
+    SignupEmailClicked,
     [EnumMember(Value = "signup")]
     Signup,
     [EnumMember(Value = "upgrade-plan")]

src/Core/Tools/Models/Business/ReferenceEvent.cs

@@ -256,7 +256,19 @@ public class ReferenceEvent
     public string? PlanUpgradePath { get; set; }
 
     /// <summary>
-    /// Used for the sign up event to determine if the user has opted in to marketing emails.
+    /// Used for the <see cref="ReferenceEventType.Signup"/> event to determine if the user has opted in to marketing emails.
     /// </summary>
     public bool? ReceiveMarketingEmails { get; set; }
+
+    /// <summary>
+    /// Used for the <see cref="ReferenceEventType.SignupEmailClicked"/> event to indicate if the user
+    /// landed on the registration finish screen with a valid or invalid email verification token.
+    /// </summary>
+    public bool? EmailVerificationTokenValid { get; set; }
+
+    /// <summary>
+    /// Used for the <see cref="ReferenceEventType.SignupEmailClicked"/> event to indicate if the user
+    /// landed on the registration finish screen after re-clicking an already used link.
+    /// </summary>
+    public bool? UserAlreadyExists { get; set; }
 }