Add database folder containing ES mappings and query configs

Lei Caorequested to merge
caolei-harvesters into main

This merge request adds the database/ folder, which contains:

  • ElasticSearch index mappings and field definitions

  • Predefined ES query templates used by the Jupyter frontend

  • Example scripts to fetch and structure query results for downstream analysis

This enables the frontend (Jupyter Notebooks) to dynamically retrieve data from ES indices and conduct real-time or batch sentiment-based filtering and visualization.

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