Base and Middle layer of Docker images need to be rebuilt periodically

[ouankou]

They are both based on Ubuntu 18.04 docker images. The upstream image changes time to time. If FreeCC images fall behind too much, it's possible that the new tutorial images can't be built successfully because the internal package repository is outdated and can't be connected anymore.

This issue won't affect the existing tutorial images as long as we don't add or update the packages in that image. We could either manually rebuild these two images or set up GitHub Actions to do that automatically.

Involved images: https://github.com/freeCompilerCamp/play-with-compiler/blob/master/dockerfiles/dind/Dockerfile.base https://github.com/freeCompilerCamp/play-with-compiler/blob/master/dockerfiles/dind/Dockerfile.middle

[ouankou]

These two docker images will be rebuilt weekly (0:00 UTC on Sunday) or there's a new commit. A GitHub Action is set up (https://github.com/freeCompilerCamp/play-with-compiler/commit/68402ea83da8fb5bd7aa8fb4e22be3deeab37cec and https://github.com/freeCompilerCamp/play-with-compiler/commit/f012103701e1f7b3996238291871aa4d52d21de1). https://github.com/freeCompilerCamp/play-with-compiler/blob/master/.github/workflows/docker-base-middle.yml

Users can always create their own tutorial images based on the latest middle layer