Add support for newline delimited JSON Content-Type (#22947)

This commit adds support for the newline delimited JSON Content-Type, which is how
the bulk, multi-search, and multi-search template APIs expect data to be formatted. The
`elasticsearch-js` client has also been using this content type for these types of requests.

Closes #22943

1 files changed, 5 insertions, 0 deletions

diff --git a/modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestMultiSearchTemplateAction.java b/modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestMultiSearchTemplateAction.java
index 6b0497e53f..30b18edb71 100644
--- a/modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestMultiSearchTemplateAction.java
+++ b/modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestMultiSearchTemplateAction.java
@@ -81,4 +81,9 @@ public class RestMultiSearchTemplateAction extends BaseRestHandler {
                 });
         return multiRequest;
     }
+
+    @Override
+    public boolean supportsContentStream() {
+        return true;
+    }
 }