Update chart.yaml with bitnami postgres

Update the postgres image to what is actually within the values.yaml

https://repo1.dso.mil/big-bang/product/packages/gitlab/-/blob/main/chart/Chart.yaml?ref_type=heads#L112

https://repo1.dso.mil/big-bang/product/packages/gitlab/-/blob/main/chart/values.yaml?ref_type=heads#L1437