Add Playfair Cipher

[jmeline]

https://www.braingle.com/brainteasers/codes/playfair.php

[federinik]

Hi @jmeline, I have a work in progress implementation, can you assign this to me?

Thank you

[federinik]

Hi @jmeline, I was looking around for Hacktoberfest 2022 and saw I never made PR for this cipher, you still intrested in it?