Paid namespace members can delete their own user record without delay

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/385

This MR adds an exception to users under paid namespaces (excluding trials) for delayed own-user account deletion introduced by https://gitlab.com/gitlab-org/gitlab/-/issues/409025+.

With the changes in this MR, there will be no 7-day delay when a user under a paid namespace deletes their own account.

How to set up and validate locally

1. Start GDK in SAAS mode (GITLAB_SIMULATE_SAAS=1 gdk start)
2. Turn on the feature flag

   $ rails console
   > Feature.enable(:delay_delete_own_user)

3. Create a new user (user_a) and a group (paid_group)
4. Create an ultimate plan subscription for the new group

   $ rails console
   > GitlabSubscription.find_by(namespace_id: <paid_group.id>).destroy # delete existing subscription if there is one
   > FactoryBot.create(:gitlab_subscription, :ultimate, namespace: Group.find(<paid_group.id>))

5. Create another new user (user_b) to delete
6. Login with user_a then add user_b to the group as a Reporter/Developer/Maintainer (as long as role is not Guest)
7. Login with user_b, go to http://localhost:3000/-/profile/account then delete the account
8. Validate that user_b is deleted a few minutes later instead after 7 days

   > User.find(<user_a.id>)
   => nil

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.