As a follow-up to #21559 and #30128, we reassign sage-env-config from the package sagelib to the package sage_conf.

(After #22731, sage-env-config is no longer required by the sage script.)

(This is preparation for allowing installation of sagelib for example in a conda environment without having to run ./configure first - see #28745, #30845.)

Part of Meta-ticket #21707: Split sage-env into 5 to clean up sage configuration

Depends on #31002

CC: @jhpalmieri @kiwifb @orlitzky @dimpase @isuruf @tobiasdiez

Component: build

Keywords: sd111

Author: Matthias Koeppe

Branch/Commit: 4b52dcf

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29850