This change adds two contexts the execute scripts against:
* SEARCH_SCRIPT: Allows to run scripts in a search script context.
This context is used in `function_score` query's script function,
script fields, script sorting and `terms_set` query.
* FILTER_SCRIPT: Allows to run scripts in a filter script context.
This context is used in the `script` query.
In both contexts a index name needs to be specified and a sample document.
The document is needed to create an in-memory index that the script can
access via the `doc[...]` and other notations. The index name is needed
because a mapping is needed to index the document.
Examples:
```
POST /_scripts/painless/_execute
{
"script": {
"source": "doc['field'].value.length()"
},
"context" : {
"search_script": {
"document": {
"field": "four"
},
"index": "my-index"
}
}
}
```
Returns:
```
{
"result": 4
}
```
POST /_scripts/painless/_execute
{
"script": {
"source": "doc['field'].value.length() <= params.max_length",
"params": {
"max_length": 4
}
},
"context" : {
"filter_script": {
"document": {
"field": "four"
},
"index": "my-index"
}
}
}
Returns:
```
{
"result": true
}
```
Also changed PainlessExecuteAction.TransportAction to use TransportSingleShardAction
instead of HandledAction, because now in case score or filter contexts are used
the request needs to be redirected to a node that has an active IndexService
for the index being referenced (a node with a shard copy for that index).
Added an api that allows to execute an arbitrary script and a result to be returned.
```
POST /_scripts/painless/_execute
{
"script": {
"source": "params.var1 / params.var2",
"params": {
"var1": 1,
"var2": 1
}
}
}
```
Relates to #27875
Martijn van Groningen