Support Docker Container

[bstoll]

This PR adds a Docker image to be published to Github Packages. It is triggered on each commit to the main branch. An example of the workflow execution is here. The example package can be seen here.

docker pull ghcr.io/bstoll/gribigo:main
...
docker run ghcr.io/bstoll/gribigo:main -h
Usage of /go/bin/rtr:
  -alsologtostderr
    	log to standard error as well as files
...

Additionally, args are added for gnmi and gribi ports to make the container useful in other environments (i.e. KNE).

[robshakir]

LGTM, thanks @bstoll!