Update expert script example with termStats (#112377)

This commit fixes compilation of the expert script example to implement
the new required method of score script making termStats available.

Author: rjernst

plugins/examples/script-expert-scoring/src/main/java/org/elasticsearch/example/expertscript/ExpertScriptPlugin.java

@@ -124,6 +124,11 @@ public boolean needs_score() {
                 return false;  // Return true if the script needs the score
             }
 
+            @Override
+            public boolean needs_termStats() {
+                return false; // Return true if the script needs term statistics via get_termStats()
+            }
+
             @Override
             public ScoreScript newInstance(DocReader docReader)
                     throws IOException {