feat: Add option to remove default stopwords from word summary

[jabahm]

This PR introduces a new feature to provide greater flexibility in word summary analysis by adding the following enhancements:

• Option to Remove Default Stopwords: A new parameter remove_default_stopwords allows users to enable or disable the removal of default English stopwords.
• Selective Stopword Retention: Added keep_stopwords parameter to retain specific stopwords even when remove_default_stopwords is enabled.

Closes #1655