Add Welsh to available languages

Add Welsh to available languages when saving translation.

Without this, the form won't by available in Welsh, FormDocuments won't
be created and the runner won't know to offer a link to the Welsh
version.

Author: thomasiles

app/input_objects/forms/welsh_translation_input.rb

@@ -41,6 +41,9 @@ def submit
     end
 
     form.welsh_completed = mark_complete
+
+    form.available_languages = %i[en cy]
+
     form.save_draft!
   end