Fix: hide redundant h2 and cta when empty state showing

What does this MR do and why?

This MR closes #429645 (closed) by hiding the container holding the Workspaces h2 and New workspace CTA button. This aligns with Pajamas' recommendation to only use one primary button per context. The h2 is hidden for better visual balance as well as being unnecessary given the Empty State component already uses an h1.

MR acceptance checklist

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

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
!

How to set up and validate locally

1. Launch the gdk
2. Navigate to the homepage
3. Open Workspaces in sidebar
4. Verify that the Workspaces title and the New workspace button are hidden when the empty state is shown and shown after creating a workspace.

• NOTE: Using workspaces with GDK requires some complicated configuration. You can also test by hardcoding isEmpty to return true in workspaces_list.vue to trigger the empty state.