Create `pet` subdocument and add it to `User` schema

[JustYourBud]

The pet subdocument will include info about a user's pet such as its name, stats, moves, etc.

Interface

pets: [{
{
  _id: number;
  name: string;
  animal: string;
  stats: {
    health: number;
    speed: number;
    strength: number;
    looting: number;
  };
  state: number;
  buff: number;
  moneyFound: number;
  battlesWon: number;
  moves: [];
}