Add basic end-to-end test for admin moderation interface (#29424)

spec/support/stories/profile_stories.rb

@@ -21,6 +21,12 @@ module ProfileStories
     click_on I18n.t('auth.login')
   end
 
+  def as_a_logged_in_admin
+    # This is a bit awkward, but this avoids code duplication.
+    as_a_logged_in_user
+    bob.update!(role: UserRole.find_by!(name: 'Admin'))
+  end
+
   def with_alice_as_local_user
     @alice_bio = '@alice and @bob are fictional characters commonly used as' \
                  'placeholder names in #cryptology, as well as #science and' \