Implement shareable Go packages for language containers

Get LGTM from Cody about [go/sdk-librarian-containers-in-go?tab=t.ft3dwbukyu66](http://goto.google.com/sdk-librarian-containers-in-go?tab=t.ft3dwbukyu66).

Implement it.