metricspi: Scrape metrics from MinIO backup storage

MinIO exposes metrics in Prometheus exposition format.  By default, it
requires an authentication token to access the metrics, but I was unable
to get this to work.  Fortunately, it can be configured to allow
anonymous access to the metrics, which is fine, in my opinion.

group_vars/metricspi/scrape.yml

@@ -218,3 +218,10 @@ vmagent_scrape_configs:
   static_configs:
   - targets:
     - burp.pyrocufflink.blue:9645
+
+- job_name: minio-backups
+  metrics_path: /minio/v2/metrics/cluster
+  scheme: https
+  static_configs:
+  - targets:
+    - burp.pyrocufflink.blue:9000