Adds dev container for PlantUML development

Introduces a development container configuration with Docker support.
Includes PlantUML VS Code extension and forwards port 8080 for local server access.

Facilitates a consistent development environment for PlantUML projects.

.devcontainer/devcontainer.json

@@ -0,0 +1,17 @@
+{
+  "name": "PlantUML Dev",
+  "build": {
+    "dockerfile": "Dockerfile"
+  },
+ "forwardPorts": [8080],
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "jebbs.plantuml"
+      ],
+      "settings": {
+        "plantuml.server": "http://localhost:8080"
+      }
+    }
+  }
+}