Setup remote container and Codespaces configuration (#17)

* Add vanilla Debian devcontainer config files

Based on:
https://github.com/microsoft/vscode-dev-containers/blob/master/containers/debian/.devcontainer

* Set Zsh as default container terminal

Zsh is already installed, so this was just a case of changing the VS
Code configuration setting.

* Use dark colour theme on remote containers

* Install shellcheck extension on remote containers

* Add docker extension on remote containers

* Add yaml extension on remote containers

* Add commented out devcontainer postCreateCommand

Added it so it's there for reference.

* Fix editor problem for git commit messages

We now check for either `code` or `code-insiders` to be the editor.

* Enable VS Code commit signing flag

All this flag does is to add `-S` when calling git commit[1] from within
VS Code.

[1] microsoft/vscode#97300 (comment)

.devcontainer/Dockerfile

@@ -0,0 +1,16 @@
+# Based on the example Dockerfile at:
+# https://github.com/microsoft/vscode-dev-containers/blob/master/containers/debian/.devcontainer/Dockerfile
+
+# Update the VARIANT arg in devcontainer.json to pick an Debian version: buster (or debian-10), stretch (or debian-9)
+ARG VARIANT=buster
+FROM mcr.microsoft.com/vscode/devcontainers/base:${VARIANT}
+
+# Configure VSCode as the default editor for git commits
+# Adapted from https://github.com/microsoft/vscode-dev-containers/blob/master/containers/codespaces-linux/.devcontainer/Dockerfile
+ARG GIT_EDITOR_SCRIPT_SOURCE="https://raw.githubusercontent.com/microsoft/vscode-dev-containers/master/containers/codespaces-linux/.devcontainer/git-ed.sh"
+RUN mkdir -p /tmp/git-ed \
+    && curl -sSL  ${GIT_EDITOR_SCRIPT_SOURCE} -o /tmp/git-ed/git-ed.sh \
+    && install -m 755 /tmp/git-ed/git-ed.sh /usr/local/bin/git-ed.sh \
+    && git config --global core.editor "/usr/local/bin/git-ed.sh" \
+# Clean up
+    && rm -rf /tmp/git-ed

.devcontainer/devcontainer.json

@@ -0,0 +1,32 @@
+{
+	"name": "Docker Container GitHub Action development",
+	"dockerFile": "Dockerfile",
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": { 
+        "terminal.integrated.shell.linux": "/bin/zsh",
+        "workbench.colorTheme": "Default Dark+",
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"timonwong.shellcheck",
+		"ms-azuretools.vscode-docker",
+		"redhat.vscode-yaml"
+	]
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Uncomment to use the Docker CLI from inside the container. See https://aka.ms/vscode-remote/samples/docker-from-docker.
+    // "mounts": [ "source=/var/run/docker.sock,target=/var/run/docker.sock,type=bind" ],
+
+    // Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "uname -a",
+
+	// Uncomment when using a ptrace-based debugger like C++, Go, and Rust
+	// "runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],
+
+	// Uncomment to connect as a non-root user. See https://aka.ms/vscode-remote/containers/non-root.
+	// "remoteUser": "vscode"
+}

.vscode/settings.json

@@ -0,0 +1,4 @@
+{
+    "git.enableCommitSigning": true,
+
+}