Add github actions

[ytsopokis]

We add github actions that:

• build and push binaries to packages
• run unit tests
• run linters (go, yaml, etc)
• build and deploy container images to ghcr

We also added:

• a devcontainer for the project
• a script (that invokes the devcontainer) to run the tests locally before pushing
• applied minor code changes for linters to pass ;)

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️