The chained input in watcher is a useful feature to
call several endpoints before execution a condition.
However it was pretty hard to modify data from a previous
input in order to be able to execute it in another input.
This commit adds a another input, called a `transform` input,
which allows you to do a transform as another input in a chained
input.
See this example
```
"input" : {
"chain" : {
"inputs" : [ <1>
{
"first" : {
"simple" : { "path" : "/_search" }
}
},
{
"second" : {
"transform" : {
"script" : "return [ 'path' : 'ctx.payload.first.path' + '/' ]"
}
}
},
{
"third" : {
"http" : {
"request" : {
"host" : "localhost",
"port" : 9200,
"path" : "{{ctx.payload.second.path}}" <2>
}
}
}
}
]
}
}
```
This allows for far more flexibility before executing the next input in a chained
one.
Original commit: elastic/x-pack-elasticsearch@3af9ba6e9b
6406c9816a