Add support for Ruby extension

[ondfisk]

This pull request adds support for the "shopify.ruby-extensions-pack" extension in the devcontainer.json file. This extension provides additional functionality for Ruby development in Visual Studio Code. By including this extension in the devcontainer.json file, it will be automatically installed when the container is created, making it easier for developers to work with Ruby code in the development environment. This change improves the development experience for Ruby developers using this repository.