Add licenses to Go SDK containers

This will be a prerequisite to publishing Go SDK containers as part of the release again. See BEAM-9685

There's tool to pull in dependency license information for a Go package: https://github.com/google/go-licenses

And once the License file from PR https://github.com/apache/beam/pull/11657 is picked up,
pkd.go.dev will also display them, https://pkg.go.dev/github.com/apache/beam/sdks/go/pkg/beam?tab=licenses