`get_external_wallet()` is not retrieving the customerRefId

[juliocepar]

Describe the bug
The method get_external_wallet() is not retrieving the customerRefId property, even though this property is set for a wallet (not null).

To Reproduce
Steps to reproduce the behavior:

1. Write the following code:

from fireblocks_sdk import FireblocksSDK
import json

with open('/path/to/secret.key', 'r') as file: # Replace '/path/to/secret.key' with a valid path
    fireblocks = FireblocksSDK(
        private_key=file.read(),
        api_key='my_api_key', # Replace 'my_api_key' with a valid API Key
        api_base_url='https://api.fireblocks.io'
    )
    my_external_wallet_id = 'aac59cad-6bc7-931c-bddf-cbc633b455ea' # A valid walletId
    ew = fireblocks.get_external_wallet(my_external_wallet_id)
    print("##### Retrieving one external wallet:")
    print(json.dumps(ew, indent=2))

    external_wallets = fireblocks.get_external_wallets()
    print("##### Retrieving all the external wallets and getting only the same retrieved one above:")
    for wallet in external_wallets:
        if wallet['id'] == ew['id']:
            print(json.dumps(wallet, indent=2))
            break

2. Run the code.

Expected behavior
It should display two dictionaries printed out, according to API specifications (https://docs.fireblocks.com/api/?python#externalwallet) and they should be exactly the same object.

Actual behavior
The obtained object by using get_external_wallet() (single) doesn't have the property customerRefId, but the obtained object by using get_external_wallets() (multiple) does have that property:

##### Retrieving one external wallet:
{
  "id": "aac59cad-6bc7-931c-bddf-cbc633b455ea",
  "name": "Ricardo_ETH-ETH_TEST-EV3K05V9CDX2",
  "assets": [
    {
      "id": "ETH_TEST",
      "status": "APPROVED",
      "address": "0x26B13e3927022988cd7D805D5bc85cD9Fc06208b",
      "tag": ""
    }
  ]
}
##### Retrieving all the external wallets and getting only the same retrieved one above:
{
  "id": "aac59cad-6bc7-931c-bddf-cbc633b455ea",
  "name": "Ricardo_ETH-ETH_TEST-EV3K05V9CDX2",
  "customerRefId": "Ricardo_ETH-ETH_TEST-EV3K05V9CDX2",
  "assets": [
    {
      "id": "ETH_TEST",
      "status": "APPROVED",
      "address": "0x26B13e3927022988cd7D805D5bc85cD9Fc06208b",
      "tag": ""
    }
  ]
}

Versions:

• Python Version: 3.9
• fireblocks-sdk version: 1.16.0