feat(docker): harden docker image

[hazcod]

This change removes the alpine docker image with an empty scratch image. This removes a bunch of attack surface which is unused anyway. Additionally it adds-in an unprivileged user such that root is no longer used to reduce attack surface.

[benbjohnson]

@hazcod Thanks for the PR. I'll have to do some testing with this. Isn't running as root inside Docker typical as the container is already sandboxed?

[hazcod]

@benbjohnson It's still a best practice not to, running as root in a container greatly increases the risk of kernel exploitation or container escape. https://dockerlabs.collabnix.com/security/Running-Containers-as-ROOT.html