Add devcontainer (#4491)

devcontainers can be used by IDEs/editors like VS Code to create a standardized development environment in a container

.devcontainer/devcontainer.json

@@ -0,0 +1,28 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/cpp
+{
+  "name": "Meshtastic Firmware Dev",
+  "build": {
+    "dockerfile": "Dockerfile"
+  },
+  "features": {
+    "ghcr.io/devcontainers/features/python:1": {
+      "installTools": true,
+      "version": "latest"
+    }
+  },
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "ms-vscode.cpptools",
+        "platformio.platformio-ide",
+      ]
+    }
+  },
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally.
+  "forwardPorts": [ 4403 ],
+
+  // Run commands to prepare the container for use
+  "postCreateCommand": ".devcontainer/setup.sh",
+}