Add C# test examples (#397)

.devcontainer/devcontainer.json

@@ -4,11 +4,20 @@
 	"name": "Rust",
 	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
 	"image": "mcr.microsoft.com/devcontainers/rust:1-1-bullseye",
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"ms-dotnettools.csharp",
+				"ms-dotnettools.csdevkit"
+			]
+		}
+	},
 	"features": {
-		"ghcr.io/devcontainers/features/dotnet:2": {},
+		"ghcr.io/devcontainers/features/dotnet:2": {
+			"version": "8.0"
+		},
 		"ghcr.io/devcontainers/features/python:1": {}
 	}
-
 	// Use 'mounts' to make the cargo cache persistent in a Docker Volume.
 	// "mounts": [
 	// 	{