Add support for building docker image

[fruch]

• add slim python based Dockerfile
• add step to github actions to publish the images

Closes: #13

[fruch]

LGTM, Should we do something with this image for releases? or it should stay without many changes?

it's a separate release cycle from scylla core, while this code is submodule inside scylla core, and get tested together with scylla core

here there would be a version (once we tag one) - in pypi and as a docker image

The docker images from this reoo shouldn't be coupled with a core release, the core has it's own cqlsh in it's own docker image.