This PR adds templating for Python versions and updates the maximum supported Python version to 3.13. The following major changes related to templating are added:
- Minimum supported Python version and list of supported versions in `setup.py` are fetched using new template generated files called `python_version.py`
- Dockerfiles for the different Python Linux builds are now template generated.
- The "Supported Python Versions" section from READMEs of ancillary and main packages have been removed
Note: All the `python_version.py` files and Linux build `Dockerfiles` except `tools/dockerfile/grpc_artifact_python_linux_armv7/Dockerfile` in the PR are generated from the respective templates.
Further non-templated additions to add support for Python 3.13:
- install scripts and artifacts for windows, macos and linux are added manually. Later, these can be templated as well.
- updated cython bounds to 3.x
- updated twine version to solve [cgi module import error](https://github.com/pypa/twine/issues/1046)
- the twine update introduces a dependency on cryptography>=2.0. But the cryptography package doesn't support 32-bit Linux images and hence `twine check` has been disabled for x86 manylinux and x86 musllinux artifacts.
Closes#37643
PiperOrigin-RevId: 678954495
Sreenithi Sridharan