Verify user invite token (#14491)

* Added functionality to verify user invite tokens and create the initial password

* Add response types

* Fail ValidateCredentialsAsync when user is not approved

* Enable user as part of initial password creating using validation token

* Adds documentation to badrequest and changed nocontent to ok, to align with other APIs

* Fixed tests and added a new one

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Co-authored-by: nikolajlauridsen <nikolajlauridsen@protonmail.ch>

src/Umbraco.Core/Security/ICoreBackOfficeUserManager.cs

@@ -20,4 +20,6 @@ public interface ICoreBackOfficeUserManager
     Task<Attempt<UserUnlockResult, UserOperationStatus>> UnlockUser(IUser user);
 
     Task<Attempt<ICollection<IIdentityUserLogin>, UserOperationStatus>> GetLoginsAsync(IUser user);
+
+    Task<bool> IsEmailConfirmationTokenValidAsync(IUser user, string token);
 }