Add some VSCode and Github Codespaces configuration files

[akosiaris]

Why: Using devcontainers for development in IDEs like VSCode or even remote environments like Github Codespaces is an emerging paradigm. One of the biggest supposed benefits is reproducibility of the development environment, hopefully negating the dreated "it works on my machine!"

What: Add a simple hierarchy of files to help future development efforts in such IDEs or remote environments

A couple of notes:

* This builds upon docker.io/clojure:temurin-21-tools-deps-bookworm for
  now, as this the linux Distro, I mostly feel comfortable with. The
  intent is to align this with the image in the main Dockerfile, namely
  docker.io/clojure:temurin-21-alpine
* It installs Calva by default, which is the Clojure enabling addon for
  VSCode. While it works very well in VSCode, I am meeting some issues
  with the REPL functionality in Github Codespaces.
* Unprivileged podman is possible, but commented out for now by default,
  as I am still evaluating how well it works with Github Codespaces.