Strictly speaking, the Qlik Sense metadata is stored in a Postgres SQL database installed when you install Sense (usually). I would not write anything there. But perhaps the OP means a different Postgres database? Then I suggest an external ETL tool rather than Sense, as already suggested, but you might need Sense to store the QVD data in a text file for that ETL process.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein