Explain the changes

1. Added an alert rule for unreachable target.

Issues: Fixed #xxx / Gap #xxx

1. JIRA: https://issues.redhat.com/browse/RHSTOR-8110
2. Core PR: Exporting replication_target_status metric to use in prometheus alert noobaa-core#9385

Testing Instructions:

1. Create obc with the replication policy (also try with namespacestore):

aayush:noobaa-operator$ cat policy.json
{ "rules": [{"rule_id": "rule-2", "destination_bucket": "<target_bucket>", "filter": {"prefix": ""}}]}
aayush:noobaa-operator$ nb obc create aayush2-obc --replication-policy ./policy.json

3. Check if objects are replicated to the target bucket.
4. Now delete the target bucket and its objects --> try to put the target bucket in unreachable state (by deleting bucket, deleting source bucket from aws/azure for namespacestore, etc.)
5. Enable prometheus dashboard using below commands and execute url localhost:9090 in the browser:

helm install prometheus prometheus-community/kube-prometheus-stack
put labels release: prometheus —> for ServiceMonitor and PrometheusRules
kubectl port-forward --namespace='default' prometheus-prometheus-kube-prometheus-prometheus-0 9090

6. Check for the NooBaaReplicationTargetUnreachable alert, also you can verify the metric value NooBaa_replication_target_status=0 (for unreachable)

• Doc added/updated
• Tests added

Summary by CodeRabbit

• New Features
  • Added alerting for unreachable replication targets. The system will now raise a warning when a replication target becomes inaccessible for 5 minutes or more, including descriptive notifications to help identify the affected source and target buckets and the storage type.

_{✏️ Tip: You can customize this high-level summary in your review settings.}