[CircleCI] Store build artifacts for python docs (#37658)
Summary:
This PR allows the build artifacts for python docs to be stored on CircieCI, which helps the reviewer to preview doc changes before merging.
The artifacts can be found in the [`ARTIFACTS` tab]( https://app.circleci.com/pipelines/github/pytorch/pytorch/162986/workflows/a969f256-3243-414f-8a02-1234b9dac149/jobs/5320907/artifacts) of the test **pytorch_cpp_doc_push**, and the website is served at https://5320907-65600975-gh.circle-artifacts.com/0/docs/index.html
This PR is inspired by rgommers's comment under https://github.com/pytorch/pytorch/pull/37419#issuecomment-621420500
> There's a CircleCI job pytorch_python_doc_push that builds the docs, however it doesn't store any artifacts for PRs. Controlled by .circleci/scripts/python_doc_push_script.sh. I think that's the only doc build (?). Not sure why it doesn't store the artifacts, that would be useful.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37658
Differential Revision: D21380094
Pulled By: ezyang
fbshipit-source-id: 1dd44bf836ebc74454f4444ae9321807dccdb313
