grafana: update datasource for PG 12+ and recent grafana versions

kwollect/grafana/postgres_datasource.yaml

@@ -6,11 +6,10 @@ datasources:
     url: localhost:5432
     database: kwdb
     user: kwuser_ro
-    password: ro
+    secureJsonData:
+      password: ro
     jsonData:
       sslmode: "disable" # disable/require/verify-ca/verify-full
       maxOpenConns: 6         # Grafana v5.4+
-      maxIdleConns: 2         # Grafana v5.4+
-      connMaxLifetime: 14400  # Grafana v5.4+
-      postgresVersion: 11
+      postgresVersion: 1200
       timescaledb: true