fix(spark): replace shared spark-events PVC with emptyDir to fix Multi-Attach error

local-path provisioner is RWO-only; attaching a single PVC to master, two
workers, history-server, and streaming pod on separate nodes causes
Multi-Attach errors. Each pod now gets its own ephemeral emptyDir for
/spark-events. Event logging confs removed from CronJobs and streaming
Deployment (logs are pod-local and do not persist across restarts).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spark-cluster/base/master.yaml

@@ -42,8 +42,7 @@ spec:
               mountPath: /spark-events
       volumes:
         - name: spark-events
-          persistentVolumeClaim:
-            claimName: spark-events
+          emptyDir: {}
 ---
 apiVersion: v1
 kind: Service