Add breadcrumb linking to dashboard page to project#new and group#new

What does this MR do and why?

This adds "Groups >" and "Projects >" as first-level breadcrumb to the New Group and New Project pages. Currently these pages only show a lonely breadcrumb "New Project/Group", linking to itself ☹

Clicking on "Groups" brings you to the Groups dashboard. Same for projects.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• http://gdk.test:3000/groups/new and http://gdk.test:3000/projects/new
• ☝ Breadcrumbs.

MR acceptance checklist

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