Add de and fr translations for sitemap field

The document type has a new field "Sitemap". The caption and the hints field for nl and en are already there. I think the caption can remain "Sitemap" for de and fr as well, but that can be checked with the translators.

The hints field must get propper de and fr translations. These are the en and nl texts:

en: The value must be a fully qualified URL and point to a sitemap.xml file.
nl: Voer een volledige URL in die verwijst naar een sitemap.xml bestand.

These values are located in the file repository/src/main/resources/translation-deltas/namespace-3.xml in the project. You will have to update 3 relevant bccm projects as well.