elasticsearch input: first attempt for including metadata
elasticsearch input:updated documentation
Fixes different issues with the elasticsearch input

- The wrong scroll id was used in processing the new data
- Made the size and scroll time configurable
- Added extra option to enable the search_type=scan ( enabled by default )
  This improves the speed but disables sorting
elasticsearch input: merged an earlier solution to this from the main branch
elasticsearch input: merged an earlier solution to this from the main branch; added support for es metadata