5-longest palindromic substring: Add Alternative Solutions

[KC10201]

Provide more optimized Expand From Center solution, and Dynamic Programming solution.

• File(s) Modified: 5-Longest-Palindromic-Substring
• Language(s) Used: Java
• Submission URL: https://leetcode.com/submissions/detail/754705006/
• • Submission URL: https://leetcode.com/submissions/detail/754736572/

[Ahmad-A0]

Thanks, @KC10201!