Use a tiniest base image for Docker

[jylenhof]

Instead of using debian as image, use a slim image

[jylenhof]

Quite some gain (Perhaps a part of the gain here is due to arm deb package not on my server, more tidy to come)

root  ~  docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
codercom/code-server-amd64 3.7.4 899c7b2ff7e8 13 minutes ago 717MB
codercom/code-server latest b425735a3231 2 weeks ago 873MB
 root  ~  

[nhooyr]

So I looked into this.

See https://stackoverflow.com/questions/59794891/how-does-debian-differ-from-debian-slim

I got

$ diff debian-stable-pkgs.txt debian-stable-slim-pkgs.txt
23,24d22
< iproute2					install
< iputils-ping					install
35,36d32
< libcap2:amd64					install
< libcap2-bin					install
40d35
< libelf1:amd64					install
53d47
< libmnl0:amd64					install
77d70
< libxtables12:amd64				install

As the additional packages. iproute2 and iputils-ping are extremely useful as a developer. We can add them in manually but I think #2488 is the way to go here.