Adding Javascript Solution for Day 15

[Nisha-Rao21]

🚀 What does this PR do?

• Adds solution for LeetCode Daily Challenge on (Day 15) in (Javascript).
• We traverse the string from left to right to check if we encounter a 1 or a 0.
• Maintaing 2 counters: one to count the numberOfOnes encountered and one to store the final result of min swaps.
• In case if we reach a 1, increment numberOfOnes counter.
• In case of a 0, minSwaps += numberOfOnes

📝 Issue Reference:

Fixes issue: #15

🔍 Checklist:

Please ensure the following before submitting your PR:

• I have placed my solution in the correct folder (solutions/dayXX/).
• My code follows clean coding practices and is efficient.
• I have added comments in my code to explain the approach.
• I have updated the README.md for the specific day with a brief explanation of my solution.
• I have tested the solution on LeetCode and it works correctly.

🔧 Solution Details:

• Language Used: Javascript
• Time Complexity: O(n)
• Space Complexity: O(1)

🌟 Additional Notes (if any):