Filter extra tags with osm_tag

[FaFre]

Since #576 we can include additional information in the results. This is a great feature, and saves from reloading of full elements a lot of times 👍
Would the data structure also allow to also include the extra tags in the already existing search-filter for osm_tag?

E.g.: api?q=berlin&osm_tag=cuisine

This would be a great addition :)

[lonvia]

The extra data is currently not indexed and thus not searchable. In any case, if we wanted to search for it, this would require some special infrastructure in the query builder. Not impossible but not very high on the TODO list at the moment.

[FaFre]

Has there been a PR recently, where another property got indexed? So I can get an idea about the effort required.