GitHub Container Registry to host public images

GitHub has just made their Container Registry **free** for **anonymous image pulling** and **public image hosting** - https://github.blog/2020-09-01-introducing-github-container-registry/

Given the GoogleCloudPlatform org already uses GitHub to host the code for these community builders it seems only natural for these images to be hosted here in a publicly available and built form, reducing friction for new users to CloudBuild and community builders. Orgs and security conscious people can still use the existing clone + build + self-host usage.