Add parameter to prefix aggs name with type in search responses (#22965)

This pull request adds a new parameter to the REST Search API named `typed_keys`. When set to true, the aggregation names in the search response will be prefixed with a prefix that reflects the internal type of the aggregation.

Here is a simple example:
```
GET /_search?typed_keys
{
    "aggs": {
        "tweets_per_user": {
            "terms": {
                "field": "user"
            }
        }
    },
    "size": 0
}
```

And the response:

```
{
    "aggs": {
        "sterms:tweets_per_user": {
            ...
        }
    }
}
```

This parameter is intended to make life easier for REST clients that could parse back the prefix and could detect the type of the aggregation to parse. It could also be implemented for suggesters.

1 files changed, 2 insertions, 1 deletions

diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
index 4a8c88b309..7fc20908e8 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java
@@ -23,6 +23,7 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentType;
@@ -268,7 +269,7 @@ public class SignificantTermsSignificanceScoreIT extends ESIntegTestCase {
 
         XContentBuilder responseBuilder = XContentFactory.jsonBuilder();
         responseBuilder.startObject();
-        classes.toXContent(responseBuilder, null);
+        classes.toXContent(responseBuilder, ToXContent.EMPTY_PARAMS);
         responseBuilder.endObject();
 
         String result = "{\"class\":{\"doc_count_error_upper_bound\":0,\"sum_other_doc_count\":0,"