[docs] Docstring Extraction has a Python-side Clang dependency - CI Workflow?

@michdolan after pushing my branch for a PR (https://github.com/scoopxyz/OpenColorIO/tree/feature/python_docstrings)
I realized that the Python script that extracts the docstrings from the headers and creates the string-literals that get referenced in the PyBind11 bindings requires Python Clang in order to traverse the source headers.

First off, that would make the `Clang` (https://pypi.org/project/clang/) Python package a dependency of the Python bindings. Are we ok with that? If not then we'd have to replicate the `mkdoc.py` behavior without the Clang package. Which I'd definitely ask for help with...

Looking at the CI GitHub workflow, I don't see a place where we control Python dependencies of our CI. I see that the bash scripts are run for the `analysis_workflow.yml` to install things like numpy for this setup, but there is no equivalent step in `ci_workflow.yml`