I assume you are forwarding the events to Logstash. You don't need to use the jdbc plugin. Logstash needs to be configured to read from beats input: https://www.elastic.co/guide/en/logstash/current/plugins-inputs-beats.html
According to the command you have pasted here you enabled the module for Filebeat. You need to run metricbeat modules enable postgresql.
Metricbeat does not provide a dashboards for PostgreSQL module.