fix: filtering in assets endpoint & update guides

[Imod7]

Issue

The endpoint /accounts/{accountId}/asset-balances no longer returns results for specific assets which means that the array query param format ?assets[]=1&assets[]=2&assets[]=3does not work as expected.
The assets[] array query params are also used in:

• /accounts/{accountId}/pool-asset-balances
  and other endpoints are using array query params and are probably affected but haven't tested them:
• /pallets/{palletId}/storage/{storageItemId}
• /contracts/ink/{address}/query

Suggested Solution

This issue is due to the upgrade from Express v4 to v5. In order to correctly handle [] in query params in v5, we need to set the default parser to extended (related resource).

Testing

Test /accounts/{accountId}/asset-balances in Polkadot Asset Hub

You can test that this change fixes the issue when connected to Polkadot Asset Hub and querying:
accounts/13Fet2MzBBUbJ2oREa7JJrswGeJPY4p7cY3Z2MC9oash8kzN/asset-balances?assets[]=1337

It returns

{
  "at": {
    "hash": "0xfb9b662bcc33e303349a640a85ce35044d38f50428284717db9ecf16a44bfc0a",
    "height": "7334813"
  },
  "assets": [
    {
      "assetId": "1337",
      "balance": "1260526400000",
      "isFrozen": "isFrozen does not exist for this runtime",
      "isSufficient": true
    }
  ]
}

which is the expected output.

Test /accounts/{accountId}/pool-asset-balances in Westend Asset Hub

You can test that this change fixes the issue when connected to Westend Asset Hub and querying:
/accounts/5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty/pool-asset-balances?assets[]=55

It returns

{
  "at": {
    "hash": "0x3853a2bafd9d3eccec5f776bc99caf333fc4f17753f0145b961b23d1fbb89eb9",
    "height": "9357129"
  },
  "poolAssets": [
    {
      "assetId": "55",
      "balance": "0",
      "isFrozen": false,
      "isSufficient": false
    }
  ]
}

which is the expected output.

[IkerAlus]

LGTM!