Change GeneralScriptException to 400 (#133659)

Errors in scripts are generally due to user errors in the script itself.
ScriptException has a 400 status code reflecting that fact, but
GeneralScriptException uses the default 500 status code. This commit
fixes GeneralScriptException to match the 400 status code of other
scripting errors.

Author: rjernst

docs/changelog/133659.yaml

@@ -0,0 +1,5 @@
+pr: 133659
+summary: Fixed GeneralScriptException to return 400 http status code
+area: Infra/Scripting
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/script/GeneralScriptException.java

@@ -11,6 +11,7 @@
 
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.rest.RestStatus;
 
 import java.io.IOException;
 
@@ -38,4 +39,8 @@ public GeneralScriptException(String msg, Throwable cause) {
     public GeneralScriptException(StreamInput in) throws IOException {
         super(in);
     }
+
+    public RestStatus status() {
+        return RestStatus.BAD_REQUEST;
+    }
 }