Create GitHub action.yml

[MPV]

What

Add a proper action.yml file for GitHub Actions support, building on the previous work by @vsoch in:

• Adding Github Action to run Container Diff #286

As per docs:

• https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runs-for-docker-container-actions

Why

So it's possible to easily use this action in your workflows, like this:

[...]
steps:
  [...]
  - uses: GoogleContainerTools/container-diff@master

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[vsoch]

Awesome!

[vsoch]

@MPV I think it would be good to have (somewhere) example usage. E.g., typically actions have minimally a table with inputs and then a YAML file example, either in a README or a file that can be easily copy pasted. I'd also recommend adding a test for it.

[MPV]

@vsoch I don't disagree. Feel free to improve/iterate upon this as you see fit.

[vsoch]

@MPV I won't have bandwidth any time soon but I can add to my TODO.

[vsoch]

@MPV please see: #402 I'm including your commits there to give credit for your contribution, and opened a new PR mostly to skip the intermediate step of PR-ing to your PR to update here. Let me know what you think about my changes, and thanks for pinging me!

[MPV]

Closing in favor of #402