Add Upgrade Modal to End of Trial UX

What does this MR do and why?

In the current Active Trial experience, users struggle to distinguish between paid and free features. This becomes particularly problematic at the end of their trial, when they have difficulty identifying the value they would lose by not upgrading. To address this problem, we are exploring adding a modal to the UX that would appear to the Owner(s) of the namespace the first time they come to GitLab following the completion of their trial.

References

Screenshots or screen recordings

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
• Sign in. Create a new group.
• Apply expired trial:

bin/rails c

Group.last.gitlab_subscription.update(trial_starts_on: 2.days.ago, trial_ends_on: 1.day.ago)

• Reload the page. Verify tracking events:

Click to expand

Sequence	Activity	se_action	se_property
1	User hovers over a Premium feature	render_premium_feature_popover_end_of_trial_modal	feature ID
2	User clicks CTA in Premium feature popover	click_cta_premium_feature_popover_end_of_trial_modal	feature ID
3	User clicks Upgrade to Premium CTA	click_upgrade_end_of_trial_modal
4	User clicks Explore paid plans CTA	click_explore_end_of_trial_modal
5	User dismisses modal	dismiss_end_of_trial_modal
6	User dismisses modal by clicking outside	dismiss_outside_end_of_trial_modal
7	User dismisses modal by clicking Esc	dismiss_esc_end_of_trial_modal
8	Modal is rendered	render_end_of_trial_modal

The modal is automatically dismissed after the first appearance. To return it back sign out, close the tab, and remove callout from the DB:

bin/rails c

Users::GroupCallout.last.destroy

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #579360