[SPARK-28929][CORE] Spark Logging level should be INFO instead of DEBUG in Executor Plugin API

### What changes were proposed in this pull request?

Log levels in Executor.scala are changed from DEBUG to INFO.

### Why are the changes needed?

Logging level DEBUG is too low here. These messages are simple acknowledgement for successful loading and initialization of plugins. So its better to keep them in INFO level.

### Does this PR introduce any user-facing change?

No

### How was this patch tested?

Manually tested.

Closes #25634 from iRakson/ExecutorPlugin.

Authored-by: iRakson <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: iRakson

core/src/main/scala/org/apache/spark/executor/Executor.scala

@@ -139,20 +139,20 @@ private[spark] class Executor(
   private val executorPlugins: Seq[ExecutorPlugin] = {
     val pluginNames = conf.get(EXECUTOR_PLUGINS)
     if (pluginNames.nonEmpty) {
-      logDebug(s"Initializing the following plugins: ${pluginNames.mkString(", ")}")
+      logInfo(s"Initializing the following plugins: ${pluginNames.mkString(", ")}")
 
       // Plugins need to load using a class loader that includes the executor's user classpath
       val pluginList: Seq[ExecutorPlugin] =
         Utils.withContextClassLoader(replClassLoader) {
           val plugins = Utils.loadExtensions(classOf[ExecutorPlugin], pluginNames, conf)
           plugins.foreach { plugin =>
             plugin.init()
-            logDebug(s"Successfully loaded plugin " + plugin.getClass().getCanonicalName())
+            logInfo(s"Successfully loaded plugin " + plugin.getClass().getCanonicalName())
           }
           plugins
         }
 
-      logDebug("Finished initializing plugins")
+      logInfo("Finished initializing plugins")
       pluginList
     } else {
       Nil