Add a command to set DirectChildrenLoaded on dir

```
$ bin/alluxio fs syncDirNextTime true /data
Successfully marked the dir /data to trigger metadata sync on next
access

$ bin/alluxio fs syncDirNextTime false /data
Successfully marked the dir /data to skip metadata sync on next access
```

pr-link: #16542
change-id: cid-78744676d83727f380d4c7a4ef7206044001a5fa

core/server/master/src/main/java/alluxio/master/file/DefaultFileSystemMaster.java

@@ -4074,6 +4074,10 @@ protected void setAttributeSingleFile(RpcContext rpcContext, LockedInodePath ino
       throws FileDoesNotExistException, InvalidPathException, AccessControlException {
     Inode inode = inodePath.getInode();
     SetAttributePOptions.Builder protoOptions = context.getOptions();
+    if (inode.isDirectory() && protoOptions.hasDirectChildrenLoaded()) {
+      mInodeTree.setDirectChildrenLoaded(
+          rpcContext, inode.asDirectory(), protoOptions.getDirectChildrenLoaded());
+    }
     if (protoOptions.hasPinned()) {
       mInodeTree.setPinned(rpcContext, inodePath, context.getOptions().getPinned(),
           context.getOptions().getPinnedMediaList(), opTimeMs);

core/server/master/src/main/java/alluxio/master/file/meta/InodeTree.java

@@ -293,9 +293,21 @@ public Map<Long, Number> getFileSizeHistogram() {
    * @param dir the inode directory
    */
   public void setDirectChildrenLoaded(Supplier<JournalContext> context, InodeDirectory dir) {
+    setDirectChildrenLoaded(context, dir, true);
+  }
+
+  /**
+   * Marks an inode directory as having its direct children loaded or not.
+   *
+   * @param context journal context supplier
+   * @param dir the inode directory
+   * @param directChildrenLoaded whether to load the direct children if they were not loaded before
+   */
+  public void setDirectChildrenLoaded(Supplier<JournalContext> context, InodeDirectory dir,
+      boolean directChildrenLoaded) {
     mState.applyAndJournal(context, UpdateInodeDirectoryEntry.newBuilder()
         .setId(dir.getId())
-        .setDirectChildrenLoaded(true)
+        .setDirectChildrenLoaded(directChildrenLoaded)
         .build());
   }
 

core/transport/src/main/proto/grpc/file_system_master.proto

@@ -473,6 +473,7 @@ message SetAttributePOptions {
   repeated string pinnedMedia = 10;
   map<string, bytes> xattr = 11;
   optional alluxio.proto.journal.XAttrUpdateStrategy xattrUpdateStrategy = 12;
+  optional bool directChildrenLoaded = 13;
 }
 message SetAttributePRequest {
   /** the path of the file */

shell/src/main/java/alluxio/cli/fs/command/FileSystemCommandUtils.java

@@ -68,4 +68,21 @@ public static void setPinned(FileSystem fs, AlluxioURI path, boolean pinned,
         .build();
     fs.setAttribute(path, options);
   }
+
+  /**
+   * Sets direct children loaded.
+   *
+   * @param fs The {@link FileSystem} client
+   * @param path The {@link AlluxioURI} path as the input of the command
+   * @param directChildrenLoaded true or false
+   */
+  public static void setDirectChildrenLoaded(FileSystem fs, AlluxioURI path,
+      boolean directChildrenLoaded)
+      throws AlluxioException, IOException {
+    SetAttributePOptions options = SetAttributePOptions.newBuilder()
+        .setRecursive(false)
+        .setDirectChildrenLoaded(directChildrenLoaded)
+        .build();
+    fs.setAttribute(path, options);
+  }
 }

shell/src/main/java/alluxio/cli/fs/command/SyncDirNextTimeCommand.java

@@ -0,0 +1,81 @@
+/*
+ * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
+ * (the "License"). You may not use this work except in compliance with the License, which is
+ * available at www.apache.org/licenses/LICENSE-2.0
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied, as more fully set forth in the License.
+ *
+ * See the NOTICE file distributed with this work for information regarding copyright ownership.
+ */
+
+package alluxio.cli.fs.command;
+
+import alluxio.AlluxioURI;
+import alluxio.annotation.PublicApi;
+import alluxio.cli.CommandUtils;
+import alluxio.client.file.FileSystemContext;
+import alluxio.exception.AlluxioException;
+import alluxio.exception.status.InvalidArgumentException;
+
+import org.apache.commons.cli.CommandLine;
+
+import java.io.IOException;
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Sync direct children next time command.
+ */
+@ThreadSafe
+@PublicApi
+public final class SyncDirNextTimeCommand extends AbstractFileSystemCommand {
+
+  private boolean mSyncNextTime;
+
+  /**
+   * @param fsContext the filesystem of Alluxio
+   */
+  public SyncDirNextTimeCommand(FileSystemContext fsContext) {
+    super(fsContext);
+  }
+
+  @Override
+  public String getCommandName() {
+    return "syncDirNextTime";
+  }
+
+  @Override
+  public void validateArgs(CommandLine cl) throws InvalidArgumentException {
+    CommandUtils.checkNumOfArgsEquals(this, cl, 2);
+  }
+
+  @Override
+  protected void runPlainPath(AlluxioURI path, CommandLine cl)
+      throws AlluxioException, IOException {
+    FileSystemCommandUtils.setDirectChildrenLoaded(mFileSystem, path, mSyncNextTime);
+    System.out.format("Successfully marked the dir %s to %s%n", path,
+        mSyncNextTime ? "trigger metadata sync on next access"
+            : "skip metadata sync on next access");
+  }
+
+  @Override
+  public int run(CommandLine cl) throws AlluxioException, IOException {
+    String[] args = cl.getArgs();
+    mSyncNextTime = Boolean.parseBoolean(args[0]);
+    runWildCardCmd(new AlluxioURI(args[1]), cl);
+    return 0;
+  }
+
+  @Override
+  public String getUsage() {
+    return "syncDirNextTime <true|false> <path>\n"
+        + "\ttrue means the next access will trigger a metadata sync on the dir"
+        + "\tfalse means the next metadata sync is disabled";
+  }
+
+  @Override
+  public String getDescription() {
+    return "Marks a directory to either trigger a metadata sync or skip the "
+        + "metadata sync on next access.";
+  }
+}