avoid too aggressive decommission in k8s batch jobs

eu-cdse/openeo-cdse-infra#185

Author: jdries

openeogeotrellis/deploy/sparkapplication_template.yaml.j2

@@ -52,6 +52,7 @@ spec:
     "spark.serializer": "org.apache.spark.serializer.KryoSerializer"
     "spark.dynamicAllocation.enabled": "true"
     "spark.dynamicAllocation.shuffleTracking.enabled": "true"
+    "spark.dynamicAllocation.executorIdleTimeout": "240s"
     "spark.decommission.enabled": "true"
     "spark.storage.decommission.enabled": "true"
     "spark.storage.decommission.rddBlocks.enabled": "true"