Upgrade postgresql-exporter to 0.9.0
Upgrade postgresql-exporter to 0.9.0

This version switches to go mod to support Go v1.16.

Changes:
https://github.com/prometheus-community/postgres_exporter/blob/master/CHANGELOG.md

Changelog: changed

gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab