Added custom config.js to e2e-environment package

This custom config.js provides all the functionality of the config package along with extending the `get` method to accept an optional second argument that will be used if the property is not found in the config file.

packages/js/e2e-environment/config/config.js

@@ -0,0 +1,32 @@
+/**
+ * External Dependencies
+ */
+const config = require( 'config' );
+
+/**
+ * Since the 'config' object is not extensible, we create an empty 'e2eConfig' object and map
+ * its prototype to the 'config' object. This allows us to extend the new 'e2eConfig' object
+ * while still having access to all the data and methods of 'config'
+ */
+const e2eConfig = Object.create( config );
+
+/**
+ *
+ * @param property { string } - the property to be fetched from the config file
+ * @param defaultValue { string | number | boolean | null } - default value if 'property' is not found
+ * @returns { string | number | boolean }
+ * @throws Error
+ */
+e2eConfig.get = ( property, defaultValue = null ) => {
+	if ( config.has( property ) ) {
+		return config.get( property );
+	} else if ( defaultValue ) {
+		return defaultValue;
+	}
+
+	throw new Error(
+		`Configuration property "${ property }" is not defined and no defaultValue has been provided`
+	);
+};
+
+module.exports = e2eConfig;