Fix issue with endless redirect

What does this MR do and why?

In an effort to have a solid test suite around the existing registration flow, we'd like to backfill the test suite.

• Invite registration flow without tasks
• Invite registration flow with tasks

And fix issue with endless redirect and add feature tests for invitation with tasks

How to set up and validate locally

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Visit any group members page with such url: groups/<group-path>/-/group_members?open_modal=invite_members_for_task
• Invite new member. Copy invitation link from logs.
• Finish onboarding and make sure you can go to the root path.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #363540 (closed)

app/controllers/registrations/welcome_controller.rb

@@ -82,12 +82,11 @@ def update_success_path
 
       if registering_from_invite?(members)
         flash[:notice] = helpers.invite_accepted_notice(members.last)
-        members_activity_path(members)
-      else
-        # subscription registrations goes through here as well
-        finish_onboarding_if_in_subscription_flow
-        path_for_signed_in_user(current_user)
+        return members_activity_path(members)
       end
+
+      # subscription registrations goes through here as well
+      path_for_signed_in_user(current_user)
     end
 
     # overridden in EE
@@ -103,9 +102,6 @@ def track_event(action); end
     def welcome_update_params
       {}
     end
-
-    # overridden in EE
-    def finish_onboarding_if_in_subscription_flow; end
   end
 end