[Feature] Next move as an arrow but only whenever there is a variation

[Vavo77]

https://lichess.org/forum/lichess-feedback/indicating-there-is-a-variation-as-arrow-on-the-board#5
..
#11962

why i requested this?

• because looking at both board & notation pane is tedious & i sometimes would like to focus only on the board..
• can work in several domains such as study, streamers when they show their games & arguing or explaining about specific position & my games analysis (specially after the good feature of "temporary moves storage")
• by this feature you will not miss any variation lines you entered before when reviewing the game.
• this feature will make it easy for a user to follow variation lines specifically if there is a lot of variation lines.
  ..
  yes i avoided to suggest the main moves to be showed as arrow on the board, because i think this would be like a spamming
  my regards..

[kraktus]

We know have variation arrows