Add test feature

Author: thecoop

plugins/examples/rescore/src/yamlRestTest/resources/rest-api-spec/test/example-rescore/30_factor_field.yml

@@ -50,6 +50,9 @@ setup:
 
 ---
 "referencing a missing field returns bad request":
+  - requires:
+      cluster_features: [ "search.rescorer.missing.field.bad.request" ]
+      reason: "Testing the behaviour change with this feature"
   - do:
       catch: bad_request
       search:

server/src/main/java/org/elasticsearch/search/SearchFeatures.java

@@ -28,9 +28,10 @@ public Set<NodeFeature> getFeatures() {
     public static final NodeFeature COMPLETION_FIELD_SUPPORTS_DUPLICATE_SUGGESTIONS = new NodeFeature(
         "search.completion_field.duplicate.support"
     );
+    public static final NodeFeature RESCORER_MISSING_FIELD_BAD_REQUEST = new NodeFeature("search.rescorer.missing.field.bad.request");
 
     @Override
     public Set<NodeFeature> getTestFeatures() {
-        return Set.of(RETRIEVER_RESCORER_ENABLED, COMPLETION_FIELD_SUPPORTS_DUPLICATE_SUGGESTIONS);
+        return Set.of(RETRIEVER_RESCORER_ENABLED, COMPLETION_FIELD_SUPPORTS_DUPLICATE_SUGGESTIONS, RESCORER_MISSING_FIELD_BAD_REQUEST);
     }
 }