Modify admin layout to only manage tenants and admins

We only want to render the account link and login items in the header.
And we want only render the Multitenancy and Administrators sections in
the admin sidebar.

We include the administrators management so it's possible to give
permissions to other users to manage tenants.

In order to restrict access to other sections by typing the URL or
following a link, we're only enabling the rest of the routes when we
aren't in the multitenancy management mode.

spec/components/layout/admin_header_component_spec.rb

@@ -35,4 +35,13 @@ describe Layout::AdminHeaderComponent do
       expect(page).not_to have_css "[data-toggle]"
     end
   end
+
+  it "does not show link to root path when multitenancy_management_mode is enabled" do
+    allow(Rails.application.config).to receive(:multitenancy_management_mode).and_return(true)
+    create(:administrator, user: user)
+
+    render_inline Layout::AdminHeaderComponent.new(user)
+
+    expect(page).not_to have_link "Go back to CONSUL"
+  end
 end