Publish a Dockerfile or include it in the standard nats-io file

[disarticulate]

trafficstars

Trying to put some containers together, and find it odd that I need go to build a tool to secure nats.

Why not provide either:

1. A binary inside the nats-io dockerfiles or
2. A Dockerfile that builds the binary.

I'm not a go programmer but certainly appreciate whenever I can build a product like this without having to install all the dev tools inside a docker or my own shell.

[ColinSullivan1]

Part of this PR is also described in https://github.com/nats-io/nats-site/issues/265