Fix python package build

[SamuelTrendio]

This simple change makes it possible to properly build the python package.

Without the __init__.py file, the ticktok_business folder is not considered a python module and not included in the distribution.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[jasonchentt]

This simple change makes it possible to properly build the python package.

Without the __init__.py file, the ticktok_business folder is not considered a python module and not included in the distribution.

We are the tiktok SDK official team and I will use another PR to fix this issue. Many thanks for your findings and comments

[jasonchentt]

The changes are already covered in another PR: https://github.com/tiktok/tiktok-business-api-sdk/pull/37, thanks!