Add workflow to build and push action images.

[paketo-bot]

Summary

This PR adds a workflow to build and push the docker images for pre-built actions. We are just starting with one image to drive out the logic: we will expand to all the pre-built images once we've proven this works.

Similarly, we're just starting with workflow_dispatch while we iterate, and once we're happy with this we can add some push/timer triggers too.

Use Cases

See #637 (and some conversation in #779) for the pain around trying to do this manually.

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).