This processor is useful when all elements of a json array need to be processed in the same way.
This avoids that a processor needs to be defined for each element in an array.
Also it is very likely that it is unknown how many elements are inside an json array.
- move ingest plugin docs to core reference docs
- move geoip processor docs to plugins/ingest-geoip.asciidoc
- add missing options tables for some processors
- add description of pipeline definition
- add description of processor definitions including common parameters
like "tag" and "on_failure"