Add devcontainer config and adjust docker compose to work with docker volumes
I personally use VSCode devcontainers for most of my dev environments, rather than installing things on my host system. I'm new to UIS DevOps and not sure what the consensus on devcontainers is here, but I find it useful to have a devcontainer config in place to allow people to start working on a repo without needing to manually follow steps to install things, and potentially have conflicts with other things installed on their host machine.
This MR adds a devcontainer config to allow a dev environment for the the repository to be automatically created by vscode (or other devcontainer-using tools). It works with both local filesystem bind mount workspaces, and named container volumes.
It also makes some adjustments to the docker-compose.yaml config, to allow the mount options to be overridden when using a devcontainer.