Extract Spark Plan "simpleString" into traces (#9645)

* Make tests explicit for physical plan field

* Extract simpleString from Spark StagePlanInfo, add to JSON payload in span

Author: charlesmyu

dd-java-agent/instrumentation/spark/src/main/java/datadog/trace/instrumentation/spark/SparkSQLUtils.java

@@ -165,6 +165,14 @@ private void toJson(JsonGenerator generator, Map<Long, AccumulatorWithStage> acc
       generator.writeStringField("node", plan.nodeName());
       generator.writeNumberField("nodeId", plan.hashCode());
 
+      String nodeDetails = plan.simpleString();
+      if (nodeDetails.startsWith(plan.nodeName())) {
+        nodeDetails = nodeDetails.substring(plan.nodeName().length()).trim();
+      }
+      if (!nodeDetails.isEmpty()) {
+        generator.writeStringField("nodeDetailString", nodeDetails);
+      }
+
       // Metadata is only present for FileSourceScan nodes
       if (!plan.metadata().isEmpty()) {
         generator.writeFieldName("meta");