Add a non-root "villas" user to the dev container

According to the VS Code documentation for the "Remote - Containers" extension, using the root account in a development container on a Linux host will apply root ownership to all files created by VS Code, even outside the container. MacOS and Windows are unaffected since they translate the file permissions. See https://code.visualstudio.com/remote/advancedcontainers/add-nonroot-user

This creates a non-root user "villas" in the container, which is given unconditional access to sudo and uses it for the VS Code development container environment, as recommended by the documentation.

VS Code should now be able to translate the UID and GID of created files on Linux.