Write a function `keyAdderUniqueVal(object, key, value)` that accepts an

object, a string to be set as a key in that object, and a value. When invoked

the function should assign the key and value arguments as a key value pair in

the object argument ONLY IF the value is not already a value for a different

key in the object. Return the mutated object.

See below for examples

let cat = { name: 'Willie', color: 'orange' };

keyAdderUniqueVal(cat, "toy", "yarn"); // => {name: "Willie", color: "orange", toy: "yarn"}

keyAdderUniqueVal(cat, "fruit", "orange"); // => {name: "Willie", color: "orange", toy: "yarn"}

console.log(cat); // { name: "Willie", color: "orange", toy: "yarn" }