vscode: add default settings for cmake

.vscode/settings.json

+{
+    "cmake.configureSettings": {
+        "OPENDHT_SANITIZE": true,
+        "OPENDHT_PROXY_CLIENT": true,
+        "OPENDHT_PROXY_SERVER": true,
+        "OPENDHT_C": true,
+        "OPENDHT_DOCUMENTATION": false
+    }
+}
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