Add devcontainer configuration for development (#65)

This PR adds a devcontainer configuration that forwards common ports
used during development including those for WebRTC. Installation of
kraftkit and updating/upgrading occur on container creation using the
`onCreateCommand` key. The latest Ubuntu LTS is used in an attempt to
maintain some parity with the build pipeline.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Add VS Code devcontainer based on Ubuntu with Docker-in-Docker,
Go/Node features, kraftkit install on create, and forwarded TCP/UDP
ports (incl. WebRTC).
> 
> - **Dev Environment**:
>   - **New `/.devcontainer/devcontainer.json`**:
> - Base image `mcr.microsoft.com/devcontainers/base:ubuntu` with
features: Docker-in-Docker, Go, Node (latest).
> - `onCreateCommand`: apt setup, add Unikraft repo, install `kraftkit`,
system upgrade.
> - Forward ports: `444` (Kernel Images API), `8080` (Web Interface),
`9222` (CDP); UDP range `56000-56100` for WebRTC.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
d028f0e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---

<!-- mesa-description-start -->
## TL;DR

Adds a devcontainer configuration to standardize the development
environment.

## Why we made these changes

To create a consistent development environment that mirrors the build
pipeline, simplifies onboarding, and automates the installation of
necessary tools like `kraftkit`.

## What changed?

- Added `.devcontainer/devcontainer.json` to define the development
environment.
- The container is based on Ubuntu LTS and includes features for
Docker-in-Docker, Go, and Node.js.
- Uses `onCreateCommand` to automatically install `kraftkit` and run
system updates on container creation.
- Forwards TCP ports `444` (API), `8080` (Web), `9222` (CDP), and the
UDP port range `56000-56100` for WebRTC.

## Validation

- [ ] Devcontainer builds and starts successfully.
- [ ] `kraftkit` is installed and available in the container's terminal.
- [ ] Forwarded ports are accessible from the host machine.

<sup>_Description generated by Mesa. [Update
settings](https://app.mesa.dev/onkernel/settings/pull-requests)_</sup>
<!-- mesa-description-end -->

Author: matthewjmarangoni

.devcontainer/devcontainer.json

@@ -0,0 +1,36 @@
+{
+	"name": "Kernel Devcontainer",
+	"image": "mcr.microsoft.com/devcontainers/base:ubuntu",
+	"features": {
+		"ghcr.io/devcontainers/features/docker-in-docker:2": {},
+		"ghcr.io/devcontainers/features/go:1": {},
+		"ghcr.io/devcontainers/features/node:1": {
+			"nodeGypDependencies": false,
+			"version": "latest"
+		}
+	},
+	"onCreateCommand": "sudo apt-get -y update && sudo apt-get -y install ca-certificates curl gnupg lsb-release && sudo mkdir -p /etc/apt/keyrings && curl -fsSL https://deb.pkg.kraftkit.sh/gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/unikraft.gpg && echo \"deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/unikraft.gpg] https://deb.pkg.kraftkit.sh /\" | sudo tee /etc/apt/sources.list.d/unikraft.list >/dev/null && sudo apt-get -y update && sudo apt-get -y install kraftkit && sudo apt-get -y upgrade",
+	"forwardPorts": [
+		444,
+		8080,
+		9222
+	],
+	"portsAttributes": {
+		"444": {
+			"label": "Kernel Images API",
+			"onAutoForward": "notify"
+		},
+		"8080": {
+			"label": "Web Interface (Neko WebRTC UI)",
+			"onAutoForward": "notify"
+		},
+		"9222": {
+			"label": "CDP (ncat Chromium)",
+			"onAutoForward": "notify"
+		}
+	},
+	// WebRTC UDP ports
+	"appPort": [
+		"56000-56100:56000-56100/udp"
+	]
+}