feat: adds mkDevOCI for generating devcontainers

[jmgilman]

This PR introduces support for generating container images that are compatible with devcontainers. It ingests a devshell and builds a compatible OCI image which can then be invoked as a devcontainer.

[blaggacao]

/cc @angerman fyi/fysa

[jmgilman]

The last commit was done entirely within the devcontainer for std! 🚀

[jmgilman]

The function has been generalized so as to not rely on vscode. By default, it creates a "generic" container which can be used like so:

docker run -it -v "$(pwd):/work" --entrypoint /bin/bash std-dev

If the vscode argument is set to true, then it will augment the container to be compatible with vscode:

devcontainer open .

[blaggacao]

Minors...