add TORCHDYNAMO_CAPTURE_DYNAMIC_OUTPUT_SHAPE_OPS (#127017)

tlparse prints failure description like this

> dynamic shape operator: aten._unique2.default; to enable, set torch._dynamo.config.capture_dynamic_output_shape_ops = True

adding os env var to set it easier for testing

Pull Request resolved: #127017
Approved by: https://github.com/jackiexu1992

torch/_dynamo/config.py

@@ -221,7 +221,9 @@ def is_fbcode():
 # break instead of capturing.  This requires dynamic_shapes to be True.
 # If you set this to True, you probably also want capture_scalar_outputs
 # (these are separated for historical reasons).
-capture_dynamic_output_shape_ops = False
+capture_dynamic_output_shape_ops = (
+    os.environ.get("TORCHDYNAMO_CAPTURE_DYNAMIC_OUTPUT_SHAPE_OPS", "0") == "1"
+)
 
 # By default, dynamo will treat all ints as backed SymInts, which means (1) it
 # will wait to see the int change over multiple runs before generalizing and