Role archives and history page

From @astrofrog:

> Somewhere (doesn't have to be too obvious necessarily) we should keep a list of people who were previously in roles, so that there is an official place we record this (because I think we should recognize past as well as current contributions)

No files, tests, or entry points are named. Inspect the existing role pages and site navigation to determine where a historical list belongs, then confirm the expected people, roles, and presentation with a maintainer; done means past role holders have an official, discoverable history page.

Written by the indexing model from the issue text.