Add labelTranslationKey, groupTranslationKey to top-nav.yaml or sidebars.yaml

[tequdev]

#2499

If the key exists but is not yet translated, it is desirable that the key be added to `@18n/[lang]/translations.yaml as null.

It may be a good idea to create a script and add a new key from top-nav.yaml or sidebars.yaml to translation.yaml.