Add mobile_optimized tag to optimized model. (#45479)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45479
Add a top level boolean attribute to the model called mobile_optimized that is set to true if it is optimized.
Test Plan: buck test //caffe2/test:mobile passes
Reviewed By: kimishpatel
Differential Revision: D23956728
fbshipit-source-id: 79c5931702208b871454319ca2ab8633596b1eb8
