Use DuckDB as a data source for Saaru

[anirudhRowjee]

As of right now, only pre-defined maps present in Saaru can be used as data sources, leaving a lot of the querying/filtering to the Templating engine. This PR implements DuckDB as a query and storage layer for the contents of your static site, eventually letting users define collections in terms of SQL queries, leaving the filtering, sorting, and other similarly expensive operations to the database.