Add Dependabot config for go.mod and package.json

[Jaro-c]

I checked and there's no .github/dependabot.yml here either. This repo has both go.mod and package.json (used for the npm-wrapper publish), and neither gets automated update PRs right now. I'd propose:

version: 2
updates:
  - package-ecosystem: "gomod"
    directory: "/"
    schedule:
      interval: "daily"
  - package-ecosystem: "npm"
    directory: "/"
    schedule:
      interval: "daily"
  - package-ecosystem: "github-actions"
    directory: "/"
    schedule:
      interval: "daily"

Split out from #19.