Named resourced stubs (meta-pytorch#1161)

Summary:


Internal
Generate stubs for all the methods generated by the decorator of `named_resources`.

Previous attempt reverted D83985902 because of autodeps issues. 
Genrule that looks at the all the named_resources and generates a file `named_resources.pyi` which is used by the test. 


Three targets added
1. `//torchx/fb:named_resources_gen`
2. `//torchx/specs:named_resources_stubs`
3. `//torchx/specs:named_resources_stubs_lib`

Use `//torchx/specs:named_resources_stubs_lib` in the test target.

Modify some named resources as well.

Differential Revision: D86111386

Author: AbishekS

torchx/specs/test/named_resources_test.py

@@ -8,7 +8,6 @@
 # pyre-strict
 
 
-import os
 import unittest
 from unittest.mock import MagicMock, patch