Add restart command

Signed-off-by: Jaida Wu <mlgmxyysd@meowcat.org>

src/main/java/emu/grasscutter/command/commands/Restart.java

+package emu.grasscutter.command.commands;
+
+import emu.grasscutter.command.Command;
+import emu.grasscutter.command.CommandHandler;
+import emu.grasscutter.game.GenshinPlayer;
+
+import java.util.List;
+
+@Command(label = "restart", usage = "restart - Restarts the current session")
+public class Restart implements CommandHandler {
+
+    @Override
+    public void onCommand(GenshinPlayer sender, List<String> args) {
+        sender.getSession().close();
+    }
+}