feat: docker build workflow

[sammcj]

• Build container image
• Publish to Github Container Registry
• Fix deprecated Dockerfile syntax
• Minor linting fixes

Tested here - https://github.com/sammcj/explainshell/actions/runs/3708331408

@idank

[sammcj]

@idank

[idank]

Looks great overall, left one minor comment. Thanks for contributing!

[idank]

Can you squash the commits please?

[sammcj]

Usually GitHub has the squash and merge when merging PRs?

If it's not showing up for some reason I'll do it in a few days as I'm away from my computer for the holidays.

[idank]

oh you're right, i haven't seen that before, merging!

happy holidays and thanks again

[idank]

It appears there's some breakage in the tests workflow, I couldn't find the cause at a quick glance, any idea what changed?

https://github.com/idank/explainshell/actions/runs/3771229887/jobs/6411513291#step:8:170