Dockerfile for static sites shouldn't be in an Node-only state

[jaredcwhite]

I was reviewing this documentation on setting up a Dockerfile, and it's strange to me that we're building assets in a Node-only environment without Ruby and not using the proper Rake task. It really should be as close to bin/bridgetown deploy as possible, as that's our canonical production build process.

Honestly I think it's a mistake we have completely separate files for Static and Dynamic as well. They should be as close to identical as possible.