[http-client-python] emit warning when name collision occurs

Since our models are mappings in Python, it's common for a name collision to occur where the API uses property names like `values` or `items` and the emitter renames this with a suffix, like `values_property` etc.

Example: https://spa.apiview.dev/review/b407cf6cfc8d4a4990ec745321da2a5c?activeApiRevisionId=29375849563d4154bb96c46a0c1dad84

This is a feature request to have the Python emitter log a warning when this happens and include a clear explanation on how to fix it in the warning message.