LC problem Separate Black and White Balls java code added

[Krushit-Babariya]

🚀 What does this PR do?

• Adds a solution for the LeetCode Daily Challenge on (October 15, 2024) in Java
• The approach calculates the minimum number of swaps needed to move all '0's to the left side of the string while maintaining the relative order of '1's.

📝 Issue Reference:

Fixes issue: #15 (Replace with the actual issue number)

🔍 Checklist:

Please ensure the following before submitting your PR:

• I have placed my solution in the correct folder (solutions/day15/).
• My code follows clean coding practices and is efficient.
• I have added comments in my code to explain the approach.
• I have tested the solution on LeetCode and it works correctly.

🔧 Solution Details:

• Language Used: Java
• Time Complexity: O(n), where n is the length of the string.
• Space Complexity: O(n), due to the character array used to store the string.

🌟 Additional Notes (if any):

• The approach efficiently tracks the number of '0's and calculates the swaps required without changing the order of '1's.