Add import mesh_tensorflow.auto_mtf for auto layout and mesh shape search

tensorflow/mesh#247

This error has been reported in the above issue.
In some versions of mesh-tensorflow, errors such as attributeError: module 'mesh_tensorflow' has no attribute 'auto_mtf' occur.
This problem can be easily solved by adding a single line of code: `import mesh_tensorflow.auto_mtf`.

Author: hyunwoongko

utils.py

@@ -8,6 +8,7 @@
 import tensorflow.compat.v1 as tf
 import tensorflow.compat.v2 as tf2
 import mesh_tensorflow as mtf
+import mesh_tensorflow.auto_mtf
 from data.encoders import fetch_encoder
 import re