Restore per-commit-head publishing of docs in CI

[phlax]

description

We lost per-commit head publishing of docs moving from circleci -> azure (#13481 )

With the new setup docs are published to eg http://storage.googleapis.com/envoy-pr/PR_ISSUE_NUMBER/docs/index.html

In circleci the docs were published as artifacts, which changed with each push to the PR

This is a feature i use a lot, it allows comparison of rendered changes as the PR progresses. It also means that links/comments to specific renderings of the docs dont become meaningless when the rendering changes (see #13490 for typical thread)

There are a couple of downsides to publishing per-commit

• the URL is more complex
• PRs use a lot more disk space

I think these problems can be mitigated - eg by using gitops-type publishing of rendered docs (see discussion #13507 (comment)), and that the advantages outweigh the problems, if we have the available disk space

refs

• ci: use azp to generate docs #13481
• docs: Update start/install section #13490
• docs/ci: Publish docs build artifacts #13507

[phlax]

also worth noting that afaict the storage.googleapis rendering is cached, so it can take a while before you see changes to the docs after rebuild