* Add support for generic OTEL_PYTHON_EXCLUDED_URLS variable
Use `OTEL_PYTHON_EXCLUDED_URLS` environment variable as a fallback of
`OTEL_PYTHON_{instrumentation}_EXCLUDED_URLS`.
* Only use generic variable when instrumentation-specific is not set
* Change wording on docs
Co-authored-by: Leighton Chen <lechen@microsoft.com>
