Add pylint-2.6.bat to prepare for migration

Bug: 1157931
Change-Id: I42d1b5be0e7983e1d8311b59e841468cc33fa378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2966637
Auto-Submit: Peter Wen <wnwen@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>

pylint-2.6.bat

+@echo off
+:: Copyright 2021 The Chromium Authors. All rights reserved.
+:: Use of this source code is governed by a BSD-style license that can be
+:: found in the LICENSE file.
+setlocal
+
+:: Ensure that "depot_tools" is somewhere in PATH so this tool can be used
+:: standalone, but allow other PATH manipulations to take priority.
+set PATH=%PATH%;%~dp0
+
+:: Defer control.
+vpython "%~dp0\pylint-2.6" %*