This ticket converts all SPKG.txt files (from an ad-hoc version of mediawiki markup) to SPKG.rst.
It adds to src/doc/bootstrap a script that generate a full list of packages that Sage uses (with links to documentation - see #27495) for the reference manual from information in build/pkgs.
Depends on #29636
CC: @jhpalmieri @kiwifb @fchapoton @dimpase
Component: documentation
Author: Matthias Koeppe
Branch/Commit: 9c7ea5f
Reviewer: Dima Pasechnik
Issue created by migration from https://trac.sagemath.org/ticket/29633