fix quantization/core/test_docs for Buck2 (#83341)
Summary:
We extract the test to its own target, fixing the relative path to the
quantization docs. This allows us to find the docs with a more simple
implementation.
Test Plan: Tested locally with buck1 and buck2.
Differential Revision: D38662169
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83341
Approved by: https://github.com/huydhn, https://github.com/seemethere, https://github.com/ZainRizvi
