content_translation: Also index translations from message catalogs

Now that we are able to search using content translation, we also want
to extend this so that columns like "group__title" can be searchable in listboxs,
but categories are usually translated with `erp5_content`, which was not indexed
in content_translation table.

Extend content translation indexing to also support translations coming from
Localizer catalog make this possible.

The only limitation I could think of is that categories will need to be reindexed
when the messages are modified in catalog.
5 jobs for feat/translated_related_keys in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

01:59:31

passed ERP5.PerformanceTest-TestRunner1

00:23:24

passed ERP5.UnitTest-TestRunner1

07:31:17

failed ERP5.CodingStyleTest-TestRunner1

07:34:23

canceled ERP5.CodingStyleTest-TestRunner1