First pass at a build Docker image gh action

[ciroque]

Proposed changes

Create a GitHub Action that builds a signed Docker image and pushes the image to Docker Hub (for now)

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)