(#348) Add .devcontainer for vscode

Fixes #348.

moduleroot/.devcontainer/Dockerfile

+FROM puppet/pdk:latest
+
+# [Optional] Uncomment this section to install additional packages.
+# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+#     && apt-get -y install --no-install-recommends <your-package-list-here>
+

moduleroot/.devcontainer/devcontainer.json

+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.140.1/containers/puppet
+{
+	"name": "Puppet Development Kit (Community)",
+	"dockerFile": "Dockerfile",
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {
+		"terminal.integrated.shell.linux": "/bin/bash"
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"puppet.puppet-vscode",
+		"rebornix.Ruby"
+	]
+
+	// 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": "pdk --version",
+}