Provide a way to reproduce our registry for air-gapped users

We currently lack a proper way for customers to reproduce 1:1 our currently published modules on registry.coder.com. While they could rely on the `main` branch, we have unpublished changes.

@bcpeinhardt suggested that we could do it the following ways:
- Publish the assets directory (every version of every modules in a `.tar.gz` file) that coder/registry-server provides as an artifact
- Publish the docker image with the registry server in it so customers could just run it themselves

I think no. 2 is the better option, but it also takes some more time and might generate more support needs.
Meanwhile, no. 1 is the fastest to get rolling so we can provide air-gapped users with something in an "it works" state, and then look into getting the work done to publish the registry server.

cc: @matifali @bpmct for input