Provide the TCK Shopping Cart Example implemented in Go as a Docker Image

[marcellanz]

As the go-support library is separated from the main CloudState repository the TCK within CloudState has to be adapted to include a build of the TCK Shopping Cart Example implemented in Go that can be used for TCK runs.

[marcellanz]

A possible way to run the TCK against well known language support libraries:

• the support library builds the TCK shopping cart example
• the example "binary" is packaged as a docker image and pushed to a public repository using a tag that relates to released main CloudState release like
  • docker.pkg.github.com/cloudstateio/go-support/cloudstate-tck:0.4.3
• the TCK tries to pull known support libraries and runs the TCK against such images

hence, the main CloudState repo, regarding this Go support, will never build language support library TCK user – functions, it pulls them as container images.

[marcellanz]

implemented with: marcellanz/cloudstate@d02fdf4

• PR on the main repo as soon as the go-support repo is merged