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

@@ -65,7 +65,7 @@ def members_activity_path(members)
     end
 
     # overridden in EE
-    def complete_to_signup_onboarding?
+    def complete_signup_onboarding?
       false
     end