add alternatives to streamlit in intro

Streamlit is only one possible library to build interactive data visualizations with - we should mention the other options and compare their advantages & disadvantages in a callout box. (e.g. Dash, Flask)

Start from the lesson introduction in the Python interactive data visualizations lesson and identify where Streamlit is presented. Add a callout box that mentions alternative libraries such as Dash and Flask and compares their advantages and disadvantages; the introduction should clearly present more than one option.

Written by the indexing model from the issue text.