Clarify lifecycle scan alert wording.

Issue: BB-740

Author: benzekrimaha

monitoring/lifecycle/alerts.yaml

@@ -57,9 +57,9 @@ groups:
     Annotations:
       zenko_service: backbeat-lifecycle-producer
       description: >-
-        Last lifecycle scan was performed more than
+        Last lifecycle scan was scheduled more than
         {{ ${lifecycle_latency_warning_threshold} | humanizeDuration }} ago.
-      summary: "Lifecycle scan not executed in time"
+      summary: "Lifecycle scan not scheduled in time"
 
   - alert: LifecycleLateScan
     Expr: |
@@ -78,9 +78,9 @@ groups:
     Annotations:
       zenko_service: backbeat-lifecycle-producer
       description: >-
-        Last lifecycle scan was performed more than
+        Last lifecycle scan was scheduled more than
         {{ ${lifecycle_latency_critical_threshold} | humanizeDuration }} ago.
-      summary: "Lifecycle scan not executed in time"
+      summary: "Lifecycle scan not scheduled in time"
 
 - name: LifecycleBucketProcessor
   rules: