Update and lightweighting of container base images

[jihyungSong]

Discussed in cloudforet-io/cloudforet#115

^{Originally posted by jihyungSong February 13, 2023}
Most Cloudforet's Core and Plugin container images are using python:3.8.

I suggest using python:3 instead of python:3.8 for image updates.
It is not just for the purpose of upgrading the python version, but for the purpose of updating the basic OS(debian) and libraries of the image. latest OS libraries can also resolve container image security vulnerabilities.

Along with this, if you use python:3-slim instead of regular python:3 , you can further lightweighting the image and reduce the size of the container image to less than half.