[CORE]: add sliding window folder

[halvaradop]

Description

After working with the Two Pointers approach, I believe it’s time to create a dedicated sliding-window folder in the repository to organize LeetCode solutions that use the Sliding Window technique.

This approach builds on the concepts from Two Pointers and is commonly used for solving more advanced problems involving subarrays, substrings, or sequences where a dynamic window is required.

Creating this folder will help structure the repository better and make it easier for users to navigate and learn progressively from Two Pointers to Sliding Window problems.