Add infra/ folder

* Add `/infra/` folder for infrastructure-related code — for instance, for the Terraform of a project and/or other infrastructure-as-code.
* See [GitHub search of repos with /infra folder](https://github.com/search?q=path%3A%2Finfra%2F*+&type=code&p=2) — 36.9k+ results.
* Please feel free to reject this issue. :)