/kind bug

The guestbook-go Dockerfile uses a relatively out of date version of golang, especially since it uses go get instead of modules and go install. This updates the base image and switches to a module-based build.

Fixes #540

I am currently awaiting CNCF-CLA Approval but I have already signed the docs and permitted organization access to my forks of kubernetes/examples and kubernetes/contributor-playground.

The reason I started this was because I found an error in Minikube Dashboard about the guestbook pods. The error occurs when Docker attempts to pull registry.k8s.io/guestbook:v3 which is using an outdated image format or manifest version. I am hoping that resolving the build issues will also result in an updated image in the public repo that will enable everyone to run guestbook-go pods on up-to-date environments but the image needed an update either way and this is something I can help with.

Here's the error on Docker Pull that shows up in Minikube Dashboard:

Failed to pull image "registry.k8s.io/guestbook:v3": [DEPRECATION NOTICE] Docker Image Format v1 and Docker Image manifest version 2, schema 1 support is disabled by default and will be removed in an upcoming release. Suggest the author of registry.k8s.io/guestbook:v3 to upgrade the image to the OCI Format or Docker Image manifest v2, schema 2. More information at https://docs.docker.com/go/deprecated-image-specs/