Add devcontainer configuration

devcontainers can be used by IDEs like VSCode to build the whole development environment in a container.
This allows you to keep dependencies, build, and all development aspects separated from any development.
It also allows contributors to instantly have a working, standardized development environment.
It also allows cloud development tools like GitHub Codespaces be automatically setup with the desired environment.

See https://containers.dev/ for more details

.devcontainer/Dockerfile

@@ -0,0 +1,6 @@
+ARG VARIANT="16-buster"
+FROM mcr.microsoft.com/vscode/devcontainers/javascript-node:${VARIANT}
+
+RUN npm install -g pnpm
+
+ENV PATH="${PATH}:./node_modules/.bin"