Automatic merge from submit-queue

Rename PetSet to StatefulSet in docs and examples.

**What this PR does / why we need it**: Addresses some of the pre-code-freeze changes for implementing the PetSet --> StatefulSet rename. (#35534)

**Special notes for your reviewer**: This PR only changes docs and examples, as #35731 hasn't been merged yet and I don't want to create merge conflicts. I'll open another PR for any remaining code changes needed after that PR is merged. /cc @erictune @janetkuo @chrislovecnm