Add a workflow to publish the container image to ghcr.io (#42423)
This PR adds a job that would allow GitHub users with the write access to publish a Docker image to the GitHub registry. The current version requires manually defining the GitHub image tag but it could be further automated in the future.
The goal of this CL is to test publishing before testing if task cluster can use the published image.
More details about publishing packages https://docs.github.com/en/packages/learn-github-packages/publishing-a-package
Issue #28903