Added modified docker file with code-server inside, modified singleuser base docker image

[andriinovak]

No description provided.

[corprew]

this looks good to me.

[igor-shubenko]

LGTM

[mvoitko]

LGTM apart from minor comments

[ttngu207]

I believe the logic in the docker-compose.yaml file needs to get updated correspondingly as well, especially the

image: datajoint/djlabhub:singleuser-${JUPYTERHUB_VERSION}-py${PYTHON_VERSION}