Translated properties are indexed in content translation table,
so nothing prevent us from using them in related keys. Since in
many places we show to user translated titles in relations, it
makes sense to also support searching and sorting in catalog.

This extends related keys syntax only for the newest syntax, so
related keys like `source__translated__title=X` would allow searching
for document who have a source relation to a document with title X.

Since any properties can be translated, if for example a property
`foo` would exist and be translatable, it would be possible to search
using `source__translated__foo=X`

This is only available when content_translation business template
is installed.