1. Adjust directory names to something that works for both cases ...

   • docker/Dockerfile currently has:
     • SAGE_ROOT=/home/sage/sage
     • SAGE_LOCAL=$SAGE_ROOT/local
   • Docker images built with tox/GH Actions (including Gitpod) and also computop/sage have:
     • SAGE_ROOT=/sage
     • SAGE_LOCAL=/sage/local
   • After this ticket:
     • SAGE_ROOT=/sage
     • SAGE_LOCAL=/opt/sage
   • CoCalc Docker image has:
     • SAGE_ROOT=/usr/local/sage
     • SAGE_LOCAL=/usr/local/sage/local

2. Script package _develop; improve installation instructions in the manual #33851: Define a script package representing "useful stuff to have on a Docker image"

3. Replace all apt-get in docker/Dockerfile by using a Docker image built using build/bin/write-dockerfile as the base image.

4. By default, docker/Dockerfile would use configure --without-system-... a lot so that CI is done against "the reference distribution"

5. Move build/bin/write-dockerfile.sh into docker/

6. Add a mechanism (environment variable) to tox -e docker... to copy SAGE_LOCAL from a given Docker image.

CC: @kliem @dimpase @embray @saraedum @slel @fchapoton @tobiasdiez @williamstein @culler @NathanDunfield

Component: docker

Keywords: ci, ContinuousIntegration, sd109

Issue created by migration from https://trac.sagemath.org/ticket/29536