Introduce envsubst for config.js, update deps (#3032)

This is the implemenation of envsubst discussed in #1756 

Documentation update will follow after merge.

tests/configs/port_variable.js.template

@@ -0,0 +1,13 @@
+/* MagicMirror² Test config sample environment set port 8090
+ *
+ * By Rodrigo Ramírez Norambuena https://rodrigoramirez.com
+ * MIT Licensed.
+ */
+let config = require(process.cwd() + "/tests/configs/default.js").configFactory({
+	port: ${MM_PORT}
+});
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = config;
+}