datastore: Replacement of the lib/pq with jackc/pgx

This change adds jackc/pgx driver as a replacement for the lib/pq driver. To reduce code changes to minimum we are using github.com/jackc/pgx/v4/stdlib at first as it provides support of the standard database/sql package, but still uses pgx underneath.

However we are still require to re-write notification listener completely as it heavily depends on the driver.

Among other changes is introduction of the glsql.StringArray that hides the actual type (depending on the driver) used to store ARRAY of TEXT elements.

Closes: #3886 (closed)