conf(vscode): add extension recommendations

.vscode/extensions.json

+{
+    "recommendations": [
+        "vscjava.vscode-java-pack",
+        "vscjava.vscode-java-debug",
+        "vscjava.vscode-maven",
+        "vscjava.vscode-java-dependency",
+        "vscjava.vscode-java-test",
+        "redhat.java",
+        "yzhang.markdown-all-in-one",
+        "shd101wyy.markdown-preview-enhanced",
+        "DavidAnson.vscode-markdownlint",
+        "jebbs.plantuml",
+        "ms-vscode.live-server",
+        "vsls-contrib.codetour"
+    ]
+}
\ No newline at end of file