`_parallel_compile_patch.py` exist in multiple places, we should use template system to generate the content.
<!--
If you know who should review your pull request, please assign it to that
person, otherwise the pull request would get assigned randomly.
If your pull request is for a specific language, please add the appropriate
lang label.
-->
Closes#34847
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/34847 from XuanWang-Amos:use_template_for__parallel_compile_patch 15b98ea826
PiperOrigin-RevId: 590262888
Xuan Wang