Added the exp_type='pg' label to all targets (#1048)

discovered by the Prometheus crunchy-collect job.
This ensures that all crunchy-collect metrics have
the exp_type='pg' label as required by the Grafana
PG dashboards included in pgMonitor v3.2.

Author: andrewlecuyer

ansible/roles/pgo-metrics/templates/prometheus-config.yaml.j2

@@ -54,3 +54,5 @@ data:
         target_label: job
         separator: ': '
         replacement: '$1$2'
+      - target_label: exp_type
+        replacement: 'pg'