Onboarding: Invite new users on store level (#5719)

* Onboarding: Invite new users

- Separates the user self-registration and invite cases
- Adds invitation email for users created by the admin
- Adds invitation tokens to verify user was invited
- Adds handler action for invite links
- Refactors `UserEventHostedService`
- Fixes #5726.

* Add permissioned form tag helper

* Better way of changing a user's role

* Test fixes

BTCPayServer/Controllers/UIServerController.Users.cs

@@ -187,8 +187,8 @@ namespace BTCPayServer.Controllers
 
                     _eventAggregator.Publish(new UserRegisteredEvent
                     {
-                        Kind = UserRegisteredEventKind.Invite,
                         RequestUri = Request.GetAbsoluteRootUri(),
+                        Kind = UserRegisteredEventKind.Invite,
                         User = user,
                         InvitedByUser = currentUser,
                         Admin = model.IsAdmin,