Add use_contact field support to Transfers API

[jim-junior]

Add use_contact field since it is now required according to the API
Currently if you use the zengapay python client to request for a transfer. The use_contact field is either not posted or is posted wrongly and the request returns an error.
https://developers.zengapay.com/#the-transfer-request-object
Nobody seemed to answer this issue #7 so i just edited the source code my self

Reproduce error

transfer.py

import os
from zengapay import Collections, Transfers


config = {
    "ZENGAPAY_ENVIRONMENT": "sandbox",
    "ZENGAPAY_BASE_URL": "https://api.sandbox.zengapay.com/v1",
    "ZENGAPAY_USER_API_TOKEN": "<API-TOKEN>"
}

collection_client = Collections(config)
transfer_client = Transfers(config)

payload = {
    # The phone number that the collection request is intended for.
    "msisdn": "<phone number>",
    "amount": 30000,  # The collection request amount.
    # Internal description or reason for this collection request and must be unique for every request.
    "external_reference": f"loantrans",
    # Textual narrative describing the transaction.
    "narration": f"Get loan trans  -",
    "use_contact": False
}
resp = transfer_client.transfer(payload)
print(resp)

Error in console

/home/junior/dev/github/zengapay/.venv/lib/python3.10/site-packages/urllib3/connectionpool.py:1043: InsecureRequestWarning: Unverified HTTPS request is being made to host 'api.sandbox.zengapay.com'. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/1.26.x/advanced-usage.html#ssl-warnings
  warnings.warn(
{'use_contact': ['The use contact field must be true or false.'], 'contact_id': ['The contact id field is required.']}