Use SDK for building Go binaries

[jahkeup]

Issue or Feature Request:

The build process for the update operator should use the same Go toolchain used throughout Bottlerocket.

This can be accomplished by subbing in the SDK container where the golang:N.N image was being used before. The license scanner (#6) should also use this image when collecting the modules into the to-be-scanned vendor/ directory.

Suggested Solution

The "golang" image can be provided as an ARG to the build commands (as is proposed in #6 for other uses - see Dockerfile.licenses). I was able to make a set of changes to do this in short order (and still support docker build -t neio:latest . at the root). Here's a gist with the set of changes.

[jahkeup]

See bottlerocket-os/bottlerocket#791 for a similar change made in setting up source inputs for bottlerocket's included Go binaries.