adding the version in `__init__`

[JiahaoYao]

In the ray-lightning, there is no version number in the __init__. i.e., https://github.com/ray-project/ray_lightning/blob/main/ray_lightning/init.py

However, in other packages, you can find this

https://github.com/ray-project/ray/blob/master/python/ray/init.py#L114

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the benefit of this, user can find the version number by calling

ray_lightning.__version__