Remove learn gitlab project creation

What does this MR do and why?

• Removes learn gitlab creation and reliance as part of #388970 (closed)
• Implements the 1st step of removing the worker https://docs.gitlab.com/ee/development/sidekiq/compatibility_across_updates.html#removing-worker-classes
• Converts get started button to pajamas ViewComponent

Screenshots

no change overall - spinning/refresh gone from onboarding page since learn gitlab is no longer created

before	after

How to set up and validate locally

note basically trying to emulate feature spec steps in ee/spec/features/registrations/saas/standard_flow_just_me_creating_project_spec.rb

Click to expand

1. Setup to simulate SaaS and restart GDK
   • Make sure Admin > Settings > General > Sign Up Restrictions match the below (no admin approval, but hard email confirmation)
2. Register as a new user.
3. Confirm email by finding the confirmation path from last User created in rails console
   • Rails.application.routes.url_helpers.user_confirmation_path(confirmation_token: User.last.confirmation_token)
4. Visit the path from the previous step.
5. You should be on the sign in page, log back in.
6. Select any 'role' and 'Just me' in the welcome form after sign up step.
7. Choose 'Create a new project'
8. Click 'Continue'
9. Fill out fields to create a group and project on the next page.
10. Click 'Create project'
11. Notice no more refresh/spinner as compared to master.
12. Click on "Ok, let's go" and verify you are dropped into the learn gitlab project and the celebrate modal pops up with confetti

MR acceptance checklist

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

Related to #388970 (closed)