Add devcontainer configuration

[jhollowe]

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