Fetch balances

curl --request GET \
  --url https://api.copper.co/platform/wallets

{
  "wallets": [
    {
      "available": "<string>",
      "balance": "<string>",
      "createdAt": "<string>",
      "currency": "<string>",
      "extra": {
        "externalAccountId": "<string>"
      },
      "locked": "<string>",
      "mainCurrency": "<string>",
      "organizationId": "<string>",
      "portfolioId": "<string>",
      "portfolioType": "custody",
      "reserve": "<string>",
      "stakeBalance": "<string>",
      "totalBalance": "<string>",
      "updatedAt": "<string>",
      "walletId": "<string>"
    }
  ]
}