Add 'Publish Docker image' Github Action and enable Dependabot for it.

[pataquets]

Finally, I gave a stab at #107 using Github Actions. 🎉

Github Action requires DOCKERHUB_USERNAME and DOCKERHUB_TOKEN (generated on DH's security settings page) to be set in the Github secrets section in the repo config.
Git pushes will trigger this Github Action to build Docker images and push them to Docker Hub:

• Git branch branchname pushes sncli:branchname image tag. Thus, sncli:master acts as an edge/unreleased/HEAD image tag. Other branches push to their respective image tags (useful for testing feature branches),
• Git tags X.Y.Z or vX.Y.X push to sncli:X.Y.Z, sncli:X.Y, sncli:X and sncli:latest.:latest tag is the default when pulling if no tag specified, so docker pull insanum/sncli pulls latest HEAD code (assuming insanum is your Docker Hub user).

Also enabled Dependabot (only for Github Actions manifests). No need to toggle or configure anything.

Also, I've noticed no tag has been pushed since a while ago. Fancy to create a release to test it out? 😉 Not required, thou, as merging will trigger it anyway. Just make sure to set secrets beforehand.

[samuelallan72]

Thanks @pataquets ! I'll defer this to @insanum though, since it requires changes to the repository's config. :)

[pataquets]

@swalladge @insanum ping

[pataquets]

@insanum anything else needed here?

[insanum]

Thank you for your effort. While I don't hack on this repo anymore and no longer use sncli... I don't want a change like this to affect this repo in the future. Isn't Docker Automations/Actions a paid service? Could you just run this off of your own fork of sncli?