Create devcontainer.json (#4377)

## Description

This PR adds a configuration for github codespaces, so that anyone can
create a codespace from this repo with forc, cargo, and the Rust & Sway
VSCode plugins installed.

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

.devcontainer/devcontainer.json

@@ -0,0 +1,16 @@
+{
+    "image": "mcr.microsoft.com/devcontainers/universal:2",
+    "features": {
+        "ghcr.io/devcontainers/features/common-utils:1": {},
+        "ghcr.io/FuelLabs/devcontainer-features/fuelup:1.0.1": {},
+        "ghcr.io/devcontainers/features/rust:1": {},
+    },
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "fuellabs.sway-vscode-plugin",
+                "rust-lang.rust-analyzer"
+            ]
+        }
+    }
+}