metadata: add new Translation app field for URL for contributions

This is a field requested from a bunch of translators so they can easily
find where to translate apps:
https://forum.f-droid.org/t/translation-field-for-app-entries/1403/5

.gitlab-ci.yml

@@ -32,6 +32,7 @@ metadata_v0:
     - cd fdroiddata
     - ../tests/dump_internal_metadata_format.py
     - sed -i
+          -e '/Translation:/d'
           -e '/kivy:\sfalse/d'
           -e '/timeout:\s/d'
           metadata/dump_*/*.yaml