Enabling metrics and graphs for Postgres (optional)

Expanding on the metrics exposed by the synapse exporter and the node exporter, the playbook enables the postgres exporter that exposes more detailed information about what's happening on your postgres database.

You can enable this with the following settings in your configuration file (inventory/host_vars/matrix.<your-domain>/vars.yml):

matrix_prometheus_postgres_exporter_enabled: true

What does it do?

Name	Description
`matrix_prometheus_postgres_exporter_enabled`	Enable the postgres prometheus exporter. This sets up the docker container, connects it to the database and adds a 'job' to the prometheus config which tells prometheus about this new exporter. The default is 'false'
`matrix_prometheus_postgres_exporter_database_username`	The 'username' for the user that the exporter uses to connect to the database. The default is 'matrix_prometheus_postgres_exporter'
`matrix_prometheus_postgres_exporter_database_password`	The 'password' for the user that the exporter uses to connect to the database. By default, this is auto-generated by the playbook
`matrix_prometheus_postgres_exporter_metrics_proxying_enabled`	If set to `true`, exposes the Postgres exporter metrics on `https://matrix.DOMAIN/metrics/postgres-exporter` for usage with an external Prometheus server (only takes effect if `matrix_nginx_proxy_proxy_matrix_metrics_enabled: true`)