docs(user-guide): clean notebook outputs (#588, #589) (#597)

Updates two user guide notebooks so committed outputs no longer show
errors or noisy warnings.

- 04_vectorizers.ipynb: Guard Azure OpenAI cells when APIs are not all
set, so the notebook does not record a ValueError traceback for a
missing endpoint (see #588).

- 11_advanced_queries.ipynb: narrow warnings.filterwarnings for redis-py
hybrid “experimental API” UserWarnings, and remove the previously saved
warning text from the Basic Hybrid Query output (see #589).

Author: hillarytoh