[KYUUBI #1825] Generate appName for Flink applications

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### _Why are the changes needed?_
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Generate Flink application names for per-job clusters and application-mode clusters with respect to the pattern in Spark engine.

This is a sub-task of KPIP-2 #1322.

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #1827 from link3280/KYUUBI-1825.

Closes #1825

c6670f9b [Paul Lin] [KYUUBI #1825] Remove `null` execution target case branch
1c093d68 [Paul Lin] [KYUUBI #1825] Set app name only if absent
ee2845f0 [Paul Lin] [KYUUBI #1825] Add the default branch for pattern matching
3d9e0928 [Paul Lin] [KYUUBI #1825] Generate appName for Flink applications

Authored-by: Paul Lin <paullin3280@gmail.com>
Signed-off-by: Kent Yao <yao@apache.org>

externals/kyuubi-flink-sql-engine/src/main/scala/org/apache/kyuubi/engine/flink/FlinkSQLEngine.scala

@@ -17,16 +17,17 @@
 
 package org.apache.kyuubi.engine.flink
 
+import java.time.Instant
 import java.util.concurrent.CountDownLatch
 
 import scala.collection.JavaConverters._
 
 import org.apache.flink.client.cli.{CliFrontend, CustomCommandLine, DefaultCLI}
-import org.apache.flink.configuration.GlobalConfiguration
+import org.apache.flink.configuration.{DeploymentOptions, GlobalConfiguration}
 import org.apache.flink.table.client.gateway.context.DefaultContext
 
 import org.apache.kyuubi.Logging
-import org.apache.kyuubi.Utils.{addShutdownHook, FLINK_ENGINE_SHUTDOWN_PRIORITY}
+import org.apache.kyuubi.Utils.{addShutdownHook, currentUser, FLINK_ENGINE_SHUTDOWN_PRIORITY}
 import org.apache.kyuubi.config.KyuubiConf
 import org.apache.kyuubi.engine.flink.FlinkSQLEngine.{countDownLatch, currentEngine}
 import org.apache.kyuubi.service.Serverable
@@ -62,6 +63,8 @@ object FlinkSQLEngine extends Logging {
   val kyuubiConf: KyuubiConf = KyuubiConf()
   var currentEngine: Option[FlinkSQLEngine] = None
 
+  private val user = currentUser
+
   private val countDownLatch = new CountDownLatch(1)
 
   def main(args: Array[String]): Unit = {
@@ -72,6 +75,24 @@ object FlinkSQLEngine extends Logging {
     try {
       val flinkConfDir = CliFrontend.getConfigurationDirectoryFromEnv
       val flinkConf = GlobalConfiguration.loadConfiguration(flinkConfDir)
+
+      val executionTarget = flinkConf.getString(DeploymentOptions.TARGET)
+      // set cluster name for per-job and application mode
+      executionTarget match {
+        case "yarn-per-job" | "yarn-application" =>
+          if (!flinkConf.containsKey("yarn.application.name")) {
+            val appName = s"kyuubi_${user}_flink_${Instant.now}"
+            flinkConf.setString("yarn.application.name", appName)
+          }
+        case "kubernetes-application" =>
+          if (!flinkConf.containsKey("kubernetes.cluster-id")) {
+            val appName = s"kyuubi-${user}-flink-${Instant.now}"
+            flinkConf.setString("kubernetes.cluster-id", appName)
+          }
+        case other =>
+          debug(s"Skip generating app name for execution target $other")
+      }
+
       val engineContext = new DefaultContext(
         List.empty.asJava,
         flinkConf,