get go bin path from go and support symlink

[jfleitz]

• uses go env for getting the actual binary path
• supports a symlink of the go binary passed in as well (e.g. --go /opt/go-patched/bin/go pointing elsewhere)

[jfleitz]

@dicej @asteurer when this one is merged, can we get a new release cut for componentize-go as well? This was causing an issue in an air-gapped environment.

Thanks!