lint: Add lint for incorrect Go compiler directives.

Created by: varungandhi-src

@jhchabran pointed out in the lang-go Slack channel today: (Slack link)

Need a linter for those // go:embed ... directives that are silently ignored :oldmanyellsatcloud:. Damn space before in between the // and go:embed ... every damn time, I forget it 🤦

As a great man once said, don't let your dreams be dreams.

Test plan

Manually ran the lint. It doesn't fail right now, but it flags errors if you remove the space from the regex.