Reland "Add auto generated documentation about atomic policy groups"

This reverts commit e43038e9048ebe94637f4d8be79dceafb795d3d8.
This relands commit 5d3ecdf99f71f71e5ae4da9ca99182d39b7034bb with a fix.

Original change's description:
> Add auto generated documentation about atomic policy groups
>
> Bug: 962669
> Change-Id: Ie6333108a9bbe06c16eeb3895b17df855b705f4e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612103
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Reviewed-by: Lutz Justen <ljusten@chromium.org>
> Commit-Queue: Yann Dago <ydago@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#668579}

TBR=thakis@chromium.org

Bug: 962669
Change-Id: Ib2d1c82c9f32257c6a7158737e4a152d5fb3b667
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663079
Commit-Queue: Yann Dago <ydago@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670465}
17 files changed