use internal fetch function of node instead external node-fetch library if node version >= v18

js/fetch.js

@@ -0,0 +1,20 @@
+/**
+ * fetch
+ *
+ * @param {string} url to be fetched
+ * @param {object} options object e.g. for headers
+ * @class
+ */
+async function fetch(url, options) {
+	const nodeVersion = process.version.match(/^v(\d+)\.*/)[1];
+	if (nodeVersion >= 18) {
+		// node version >= 18
+		return global.fetch(url, options);
+	} else {
+		// node version < 18
+		const nodefetch = require("node-fetch");
+		return nodefetch(url, options);
+	}
+}
+
+module.exports = fetch;