Build an Optional Arguments Sum Function

In this lab you will build a function that accepts up to two arguments, and sum them, but if there is only one argument returns a function that waits for the second number to sum. **Objective:** Fulfill the user stories below and get all the tests to pass to complete the lab. **User Stories:** 1. Create a function `addTogether`. 2. If the function receives two arguments, the function should return the sum of the two arguments. 3. If only one argument is provided, `addTogether` should return a function. - When the returned function is called with a single argument, it should return the sum. ```js const sumTwoAnd = addTogether(2); sumTwoAnd(3); // 5 ``` 4. If either argument isn't a valid number, return `undefined`.