Add PL/PRQL extension

PRQL is an opportunity to make SQL more intuitive -- adding the PRQL extension could thus be very helpful for Supabase users!

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From Readme:

PRQL in PostgreSQL!

PL/PRQL is a PostgreSQL extension that lets you write functions with PRQL. The extension supports PostgreSQL v12-16 on Linux and macOS.

What is PRQL?

PRQL (Pipelined Relational Query Language) is an open-source query language for data manipulation and analysis that compiles to SQL. PRQL introduces a pipeline concept (similar to Unix pipes) where data is transformed line-by-line. The sequential series of transformations reduces the complexity often encountered with nested SQL queries and makes your data manipulation logic easier to read and write.