Support versions besides buster

[Coronon]

Hi there, I really love all the work by the dart team, Dart really has become one of my favorite languages (also outside of Flutter).

I am wondering why there are only buster-slim images in this repo - I require newer versions of many packages. Personally, I just copied the entire Dockerfile into my repo and changed buster -> sid, but it would be awesome to have them directly in here.

FROM dart:stabel-sid or something like that :)

[bytesizedwizard]

Upvoting! Not sure about if there are any technical challenges but would also love to see an alpine flavored image for the dart sdk.

[athomas]

Not exactly what's being asked here, but we're upgrading to bullseye:
#77

In general, we follow the latest Debian stable, based on https://dart.dev/get-dart#linux.