Improve local docs preview to not require login

[Eric-Arellano]

Currently, #1 requires log in to IBM Cloud. While that unblocks our core maintainers from making progress on the docs, it's important to open source that anyone can build the docs.

Fixing this looks like releasing a public Docker image that anyone can use, rather than requiring login to access it.

[Eric-Arellano]

The Docker image is now ready to go. We now need to figure out where to publish (Dockerhub?) and ensure security is okay.