Add duo seat assignment task to learn gitlab

What does this MR do and why?

Add duo seat assignment task to learn gitlab

• add to learn gitlab page which requires a new db column and all the fixins.
• see #522000 (closed)

Changelog: other EE: true

Screenshots or screen recordings

not complete	completed	full cycle
		Screen_Recording_2025-03-25_at_3.32.56_PM

How to set up and validate locally

1. Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
2. create a group and then a project in that group
3. In the gitlab admin UI, edit the group to be on an ultimate trial(admin -> groups -> edit your group)
4. In rails console, change the trial, trial start and end date for the group

   Group.last.gitlab_subscription.update_columns(trial_starts_on: Date.today, trial_ends_on: 30.days.from_now, trial: true)

5. Add a duo enterprise trial to that namespace in the rails console

n = Group.last
add_on = ::GitlabSubscriptions::AddOn.where(name: ::GitlabSubscriptions::AddOn.names[:duo_enterprise]).last
::GitlabSubscriptions::AddOnPurchase.create(add_on: add_on, namespace: n, quantity: 1, started_at: Time.current, expires_on: 30.days.from_now, purchase_xid: SecureRandom.hex(16), trial: true, organization_id: 1)

6. Start onboarding in rails console

n = Group.last
::Onboarding::Progress.onboard(n)

7. Go to the project page for the new project and select Learn GitLab from the sidebar

MR acceptance checklist

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Related to #522000 (closed)