chore(tools): break tools out into a separate module

[jsternberg]

This change breaks the tools out into a separate module so that we can
continue using go modules for pinning go-based dependencies, but to
avoid having these modules become part of our external dependencies.

The gotool.sh script is added to make it easy to run modules within
the tool directory while ensuring the scripts still get executed in the
current directory rather than inside of the tools directory.

Fixes #2040.

Done checklist

• docs/SPEC.md updated
• Test cases written

[affo]

Got it, brilliant

[affo]

This is great, thank you @jsternberg for this. But I have one question.

I have nothing against this implementation, but, I wonder, why don't you implement what gotools.sh does directly in a func main in internal/tools/tools.go?

Wouldn't it be more maintainable and easy to understand? I mean, more linear.

Something like:

func main() {
        dir := os.Args[1]
        goModule := os.Args[2]
        args := os.Args[3:]
	cmd := exec.Command("go", "run", goModule, args...)
        cmd.Dir = dir
	err := cmd.Run()
	log.Printf("Command finished with error: %v", err)
}

and gotool.sh:

cd $tools_dir && go run $(pwd) "$@"

[affo]

After reading my previous comment, I realized I like more this current solution, never mind 😅