Add devcontainer configuration with Java 8 and Maven support

Also added vscode recommended extensions for Java development.

Author: jbrejner

.devcontainer/devcontainer.json

@@ -0,0 +1,20 @@
+{
+    "name": "Dev Container (1-8-jdk-bullseye)",
+    "image": "mcr.microsoft.com/devcontainers/java:1-8-jdk-bullseye",
+
+    "features": {
+        "ghcr.io/devcontainers/features/java:1": {
+            "version": "8",
+            "installMaven": true
+        }
+    },
+
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "vscjava.vscode-java-pack"
+            ]
+        }
+    },
+    "postCreateCommand": "java -version"
+}