Add an option to set FEN

[LabinatorSolutions]

Adding a feature to set the FEN is highly important to many chess players.

FEN stands for "Forsyth-Edwards Notation." It is a standard method for describing chess positions using simple text.

• Read more about FEN: https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation https://www.chessprogramming.org/Forsyth-Edwards_Notation