Allow platform admins to change user auth in the UI

So we do not have to go into the db when we need to change user
auth.

We do not allow this for users who use webauthn. We do not want to
enable security downgrade for those users.

app/navigation.py

@@ -79,6 +79,7 @@ class HeaderNavigation(Navigation):
         },
         'platform-admin': {
             'archive_user',
+            'change_user_auth',
             'clear_cache',
             'create_email_branding',
             'create_letter_branding',