[ATMOSPHERE-440] chore: Add loki rule to delect Nova cell down (#1966)

fix #490
Reviewed-by: Oleksandr K.
diff --git a/roles/loki/vars/main.yml b/roles/loki/vars/main.yml
index d46ec76..82479df 100644
--- a/roles/loki/vars/main.yml
+++ b/roles/loki/vars/main.yml
@@ -73,6 +73,13 @@
       openstack-control-plane: enabled
     persistence:
       size: 256Gi
+    extraVolumeMounts:
+      - name: rules
+        mountPath: /var/loki/rulestorage/fake
+    extraVolumes:
+      - name: rules
+        configMap:
+          name: loki-alerting-rules
   write:
     replicas: 0
   read:
@@ -88,3 +95,21 @@
       openstack-control-plane: enabled
   lokiCanary:
     enabled: false
+  extraObjects:
+    - apiVersion: v1
+      kind: ConfigMap
+      metadata:
+        name: loki-alerting-rules
+        labels:
+          loki_rule: "atmosphere"
+      data:
+        loki-alerting-rules.yaml: |-
+          groups:
+            - name: additional-loki-rules
+              rules:
+                - alert: NovaCellNotResponding
+                  expr: 'count_over_time({pod_label_component="compute"} |= "not responding and hence is being omitted from the results" [1m]) > 0'
+                  labels:
+                    severity: critical
+                  annotations:
+                    summary: Nova Cell is not responding. It can cause port deletion in CAPI.