Filtering of extra tags

[FaFre]

Draft PR for filtering of extra tags, related to #592.

So far it only enables filtering on the existence of keys inside the extra-tag object. Extra tags has been introduced via #576.

Example: http://localhost:2322/api?q=monaco&extra_key=wikidata&extra_key=wikipedia Will only return elements with wikidata or wikipedia tags in extra. Behavior is similar to osm_key.

ToDo:

• So far only wikipedia and wikidata gets indexed in elastic, because I don't know how to make it dynamic for all properties inside extra. If the mapping has to get done explicitly, all the extra tags can be found here: https://taginfo.openstreetmap.org/projects/nominatim#tags
• No tests has been written yet (I'm not a java developer and don't want to deal with the tests for now...)

[phamtai97]

Any update PR? We need to your feature to query by extra tags because we has add some tags to extra-tag and want to search by it?