[KYUUBI #XXXX] Do not block server shutdown on batch sessions

Batch sessions are handles to jobs submitted to external clusters
(YARN/K8s). The actual computation runs on the cluster and continues
regardless of Kyuubi server state. Including batch sessions in the
shutdown wait loop caused the server to hang indefinitely when long-
running batch jobs were active.

Introduces `closeOnServerStop` on the Session trait (default: true,
backward-compatible). KyuubiBatchSession overrides it to false.
ServiceDiscovery.stopGracefully now waits only for sessions where
closeOnServerStop is true.

Author: turboFei

kyuubi-common/src/main/scala/org/apache/kyuubi/session/Session.scala

@@ -97,4 +97,6 @@ trait Session {
   def closeExpiredOperations(): Unit
 
   def isForAliveProbe: Boolean
+
+  def closeOnServerStop: Boolean = true
 }

kyuubi-ha/src/main/scala/org/apache/kyuubi/ha/client/ServiceDiscovery.scala

@@ -66,11 +66,13 @@ abstract class ServiceDiscovery(
 
   // stop the server genteelly
   def stopGracefully(isLost: Boolean = false): Unit = {
-    var activeSessionCount = fe.be.sessionManager.getActiveUserSessionCount
-    while (activeSessionCount > 0) {
-      info(s"$activeSessionCount connection(s) are active, delay shutdown")
+    var blockingSessionCount =
+      fe.be.sessionManager.allSessions().count(_.closeOnServerStop)
+    while (blockingSessionCount > 0) {
+      info(s"$blockingSessionCount connection(s) are active, delay shutdown")
       Thread.sleep(TimeUnit.SECONDS.toMillis(10))
-      activeSessionCount = fe.be.sessionManager.getActiveUserSessionCount
+      blockingSessionCount =
+        fe.be.sessionManager.allSessions().count(_.closeOnServerStop)
     }
     isServerLost.set(isLost)
     gracefulShutdownLatch.countDown()

kyuubi-server/src/main/scala/org/apache/kyuubi/session/KyuubiBatchSession.scala

@@ -229,4 +229,6 @@ class KyuubiBatchSession(
     EventBus.post(sessionEvent)
     traceMetricsOnClose()
   }
+
+  override def closeOnServerStop: Boolean = false
 }