[API] Leaderboard pagination support

[def750]

Since API is getting "rewrite", I'd like to propose adding pagination to leaderboard route /players/leaderboard
This would help in frontend implementation of leaderbaords since by default you can display up to 100 results from specific leaderboards and making pagination require changing code of above API route or creating another one.

[cmyui]

pagination is something i'd not only like to add to all appropriate public endpoints, but perhaps even in gulag's internal library/api