Added Solution to Challenge (#19372)

Added a Solution to "Basic Data Structures: Generate an Array of All Object Keys with Object.keys()" 's "Get a Hint" documentation.

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/generate-an-array-of-all-object-keys-with-object.keys.english.md

@@ -72,6 +72,8 @@ console.log(getArrayOfUsers(users));
 <section id='solution'>
 
 ```js
-// solution required
+function getArrayOfUsers(obj) {
+  return Object.keys(users);
+}
 ```
 </section>