Fix the default value of side in torch.searchsorted (#120066)
Fixes #119999, currently the [doc](https://pytorch.org/docs/stable/generated/torch.searchsorted.html#torch.searchsorted) shows the default value of `side = "left"`
<img width="600" alt="Screenshot 2024-02-16 at 10 36 08 AM" src="https://github.com/pytorch/pytorch/assets/7495155/e7d159aa-4985-4f50-9d81-6e71c3116c0d">
while the [implementation ](https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/native/native_functions.yaml#L11247) gives the default value of `side = c10::nullopt`.
- fix the [torch doc](https://github.com/pytorch/pytorch/blob/main/torch/_torch_docs.py#L13782) such that the default value of side is None.
- fix the [comment in cpp](https://github.com/pytorch/pytorch/blob/4dc75f9084b6c1ea063278797ee57e2533b5353d/aten/src/ATen/native/Bucketization.cpp#L19) such that the default value of side is None.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120066
Approved by: https://github.com/malfet
