A sample pure-Go server and docker config to deploy it

• This sample builds a simple pure-Go server and a docker image to deploy it.
• Because this leverages the cross-compile feature, you can run this sample on Mac and Windows as well as Linux.
• CGO_ENABLED=0 is the easiest way to generate a statically-linked binary in Go if you do not use cgo.
• CGO_ENABLED=0 is necessary if you use net package in linux.
• The root image of the docker image is Alpine Linux, not scratch because we want to install ca-certificates to the docker image. Without ca-certificates, your golang program can not connect to external servers over HTTPS.
• Please note that you may need to install additional things to your docker image if your program uses other Go packages. A statically linked binary does not necessarily means it does not have any dependencies to other files.
• Although the deployment of Go binary is relatively easy compared to other languages such as Java and Python, the deployment of a binary is still a tricky task because it's not trivial to fully understand what your program actually depends on.