```
Chained input for now works like this
{
"chain" : [
{ "first" : { "simple" : { "foo" : "bar" } } },
{ "second" : { "simple" : { "spam" : "eggs" } } }
]
```
This allows to access the payload via ctx.payload.first.foo for example
The array notation is needed to guarantee order, as JSON itself does not guarantee
order of objects.
Closeselastic/elasticsearch#353
Original commit: elastic/x-pack-elasticsearch@7ab32c43a8