[XNNPACK] Enable S8 Operators (#97386)
Enabling S8 Operators for quantized Clamp.
This is only for clamp nodes by themselves. I believe once they are fused with the previous node they are no longer needed
Differential Revision: [D43901200](https://our.internmc.facebook.com/intern/diff/D43901200/)
**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D43901200/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97386
Approved by: https://github.com/salilsdesai
