Update 0104: Add iterative DFS solution (javascript)

[eunicode]

• File(s) Modified: javascript/0104-maximum-depth-of-binary-tree.js
• Language(s) Used: javascript
• Submission URL: https://leetcode.com/problems/maximum-depth-of-binary-tree/submissions/973022625/

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This PR adds a javascript solution using iterative DFS for 104. Maximum Depth of a Binary Tree.

The javascript solution file has a recursive DFS solution and a BFS solution, but it does not have an iterative DFS solution. This PR will add an iterative DFS solution.

The NeetCode video for this problem provides an explanation and Python code for the iterative DFS solution, so it will be helpful to provide an iterative DFS solution in javascript as well.