Merge PR #40530 into master

* refs/pull/40530/head:
	doc/releases: reorg
	doc/releases/releases.yaml: add missing releases
	admin/build-doc: do not rebuild venv every time
	doc/releases/releases.yaml: add 16.2.0
	doc/releases: move 'active-releases' tag
	doc/releases: add major headings for releases

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>
Reviewed-by: Josh Durgin <jdurgin@redhat.com>
Reviewed-by: Kefu Chai <kchai@redhat.com>
Reviewed-by: Zac Dover <zac.dover@gmail.com>