add postgres exporter

Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>

roles/postgres_exporter/templates/postgres_exporter.service.j2

@@ -0,0 +1,14 @@
+[Unit]
+Description=PostgresExporter
+
+[Service]
+TimeoutStartSec=0
+User={{ bin_name }}
+ExecStart={{ bin_path }} --web.listen-address={{ host.ip }}:{{ bind_port }} {{ options }}
+Environment="DATA_SOURCE_URI=localhost:5432/postgres?sslmode=disable"
+Environment="DATA_SOURCE_USER={{ db.user }}"
+Environment="DATA_SOURCE_PASS={{ db.password }}"
+
+[Install]
+WantedBy=multi-user.target
+