Added VS Code Devcontainer

Added `.devcontainer/devcontainer.json` with the definition of a docker
image containing all the required packages to run and test the
`tools/build_documentation.sh`-file.

Simply build and connect to this dev container; mount the folder into
the dev container.

Author: Anton Schwarz

.devcontainer/devcontainer.json

@@ -0,0 +1,30 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/docker-in-docker
+{
+	"name": "Rucio-Docs",
+	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+	"image": "mcr.microsoft.com/devcontainers/base:bullseye",
+
+	"features": {
+		"ghcr.io/devcontainers/features/docker-in-docker:2": {
+			"version": "latest",
+			"enableNonRootDocker": "true",
+			"moby": "true"
+		},
+		"ghcr.io/devcontainers/features/node:1": {},
+		"ghcr.io/devcontainers/features/python:1": {},
+		"ghcr.io/devcontainers/features/ruby:1": {}
+	}
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "docker --version",
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}