Message 364264 - Python tracker

Given Ernest's comment in https://github.com/python/cpython/pull/15288#issuecomment-579476340 about the limitations of Netlify (1000 build minutes per month), it doesn't seem like Netlify will be a viable alternative.

Instead, I've added a PR (https://github.com/python/cpython/pull/19025) that takes an alternative approach. It uses GitHub Actions to deploy the docs to the gh-pages branch, then adds a comment to the PR with a link to the deploy preview.

The way this works is that the gh-pages branch has subfolders with the SHA of each commit, and each deploy preview is deployed to each subfolder.

I've enabled this on my fork of cpython -- here's an example PR on my fork: https://github.com/epicfaace/cpython/pull/7