This PR:
- Fixes the xds-protos Python package, which was broken when the `udpa`
submodule was removed
- This required re-adding the protoc-gen-validate submodule
- Adds non-Bazel tests for xds-protos and all of its dependent packages
- Versions xds-protos the same way as the rest of the Python packages
- Fixes Python 3.11 support in `run_tests.py`, which is necessary for
the testing mentioned above
CC @sergiitk You won't be able to consume this in the interop tests
until it makes it into a release. I'm thinking I'll want to backport
this to the 1.57.x branch to make that happen faster.
CC @drfloob to inform him about the likely backport.
Richard Belleville