Add missing tiers to license-gated Feature catalog nav items

What does this MR do and why?

Some license-gated sidebar items don't set a tier, so the Feature catalog labels them "Free" even though they require a paid plan. This MR adds the missing tiers, using tier_for with the licensed feature each item's gate checks:

Item	Scope	Licensed feature	Tier
Epic boards	Group	epics	Premium
Group wiki	Group	group_wikis	Premium
Virtual registry	Group	packages_virtual_registry	Premium
Requirements	Project	requirements	Ultimate

The only UI change is the tier label in the Feature catalog card footer for these four items. tier isn't read anywhere else, so the sidebar, pins, search and AI search are unaffected. The project wiki is unchanged, since it's available on every tier.

EpicsMenu#boards_menu_item already sets tier_for(:epics), so only WorkItemEpicsMenu needed the change.

References

• Closes https://gitlab.com/gitlab-org/gitlab/-/work_items/632719
• Part of https://gitlab.com/gitlab-org/gitlab/-/work_items/631003

Screenshots or screen recordings

Before	After
Epic boards, Group wiki, Virtual registry and Requirements cards show "Free"	They show "Premium" / "Ultimate"

How to set up and validate locally

1. In GDK, use a group with a Premium, Ultimate or trial license

2. On the group, select Feature catalog in the sidebar to open the modal.

3. Search for Epic boards, Wiki and Virtual registry (if virtual registries are available on your GDK), and check each card's footer. It should show Premium.

4. Open the Feature catalog on the project and search for Requirements. The card's footer should show Ultimate.

5. Run the specs:

   bin/rspec ee/spec/lib/sidebars/groups/menus/work_item_epics_menu_spec.rb \
     ee/spec/lib/sidebars/groups/menus/wiki_menu_spec.rb \
     ee/spec/lib/ee/sidebars/groups/menus/packages_registries_menu_spec.rb \
     ee/spec/lib/ee/sidebars/projects/menus/issues_menu_spec.rb \
     ee/spec/lib/ee/sidebars/projects/menus/work_items_menu_spec.rb

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