Give players the option to play against either FSF or YaneuraOu

[Eventlesstew]

https://lishogi.org/forum/general-shogi-discussion/i-am-struggling-against-the-level-2-bot-and-its-killing-my-enjoyment-of-the-game#8

I think there should be a separate dropdown option that allows players to play AI Shogi games against either Fairy Stockfish or YaneuraOu (Labelled as Expert) since YaneuraOu is a bit too much of a challenge to be a Level 2 bot. (It's more like level 4-5.)