[Quant][pt2e] torch.mean and ReLU6 (#98984)
Add nn.Module ReLU6 in addition to functional relu6.
Also add torch .mean to quantization config
Differential Revision: [D44901038](https://our.internmc.facebook.com/intern/diff/D44901038/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98984
Approved by: https://github.com/jerryzh168
