Add breadcrumbs to app/views/admin/sessions/two_factor.html.haml

We now need breadcrumbs on every page in GitLab. The breadcrumbs have been specifically hidden in this file so we need to first work out why, then work out how to add them on. It may be that this file has hidden the breadcrumbs for good reason and therefore nothing needs to be done here other than closing out the issue with an explanation of why it needs to stay hidden.

Please use the breadcrumbs helper, or GlBreadcrumb to stay Pajamas compliant.

• File: app/views/admin/sessions/two_factor.html.haml
• Rails helper: app/helpers/breadcrumbs_helper.rb
• Vue Component: <GlBreadcrumb />