Show breadcrumb on "Enter admin mode" page

What does this MR do and why?

This implements Add breadcrumbs to app/views/admin/sessions/new... (#395046 - closed).

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable admin mode for your instance first.
2. Sign out and in again. Now admin mode should be fully enabled. I assume you use the root user in your GDK.
3. Now try to enter /admin or use the main menu.
4. You should see the "Enter admin mode", now with the breadcrumbs visible.

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.