Add cancellation support to Spark pipeline execution

Author: tkaymak

runners/spark/4/src/main/java/org/apache/beam/runners/spark/structuredstreaming/SparkStructuredStreamingPipelineResult.java

@@ -113,6 +113,7 @@ public MetricResults metrics() {
 
   @Override
   public PipelineResult.State cancel() throws IOException {
+    pipelineExecution.cancel(true);
     offerNewState(PipelineResult.State.CANCELLED);
     return state;
   }