Postgresql: Fix variable interpolation logic when the variable has multiple values (#114058)
* fix the variable interpolation
* add jest config to grafana-sql
* fix broken tests
* add variable interpolation tests
* lint
* apply fix only to postresql datasource
(cherry picked from commit 0291f6d1e7)
Co-authored-by: ismail simsek <ismailsimsek09@gmail.com>