hosts: Add mtrcs0.p.r

*mtrcs0.pyrocufflink.red* is a Raspberry Pi CM4 on a Waveshare
CM4-IO-BASE-B carrier board with a NVMe SSD.  It runs a custom OS built
using Buildroot, and is not a member of the *pyrocufflink.blue* AD
domain.

*mtrcs0.p.r* hosts Victoria Metrics/`vmagent`, `vmalert`, AlertManager,
and Grafana.  I've created a unique group and playbook for it,
*metricspi*, to manage all these applications together.

group_vars/metricspi/alerts.yml

@@ -0,0 +1,48 @@
+vmalert_rules:
+  groups:
+  - name: default alert
+    rules:
+    - alert: DiskUsage
+      expr: >-
+        sum(collectd_df_df_complex{type!="free"}) by (instance, df) / sum(collectd_df_df_complex{df!="var-log"}) by (instance, df) > .75
+        or sum(collectd_df_df_complex{type!="free"}) by (instance, df) / sum(collectd_df_df_complex{df="var-log"}) by (instance, df) > .95
+      for: 2h
+    - alert: TheWebsiteIsDown
+      expr: >-
+        probe_success{job="websites"} == 0
+      for: 10m
+    - alert: Missing Metrics
+      expr: >-
+        up{instance!~"vmhost.*"} == 0
+      for: 10m
+    - alert: NUT is offline
+      expr: >-
+        absent(collectd_nut_percent)
+  
+  - name: Bitwarden
+    rules:
+    - alert: vaultwarden is not running
+      expr: >-
+        collectd_processes_ps_count_processes{processes="vaultwarden"} < 1
+      for: 5m
+  
+  - name: Active Directory
+    rules:
+    - alert: samba is not running
+      expr: >-
+        collectd_processes_ps_count_processes{processes=~"samba|smbd|winbindd|krb5kdc"} < 1
+      for: 5m
+  
+  - name: Graylog
+    rules:
+    - alert: unprocessed messages
+      expr: >-
+        org_graylog2_journal_entries_uncommitted > 100
+      for: 1h
+  
+  - name: mdraid
+    rules:
+    - alert: mdraid missing disk
+      expr: collectd_md_md_disks{type="missing"} != 0
+    - alert: mdraid failed disk
+      expr: collectd_md_md_disks{type="failed"} != 0