Want to add Longest Palindromic Substring code

[yashjaiswal5859]

I want to add Longest Palindromic Substring code which will be my 1st contribution to hacktoberfest. @fineanmol please assign this issue to me.

thanks!

[fineanmol]

@yashjaiswal5859 Please Star ⭐️ the repo to earn 'hacktober-accepted' label for the event.\nMeanwhile, if you want to work on this issue, please raise a PR, and we will review and merge it.