Change duplicated rules names (#504)

## Issue
Some rules has duplicated names that can be a little bit confusing. 

## Solution
This PR separate into different names to be more clear with the alert
rule expression and adds spaces between alerts to increase readability.

src/alert_rules/prometheus/prometheus_alerts.yaml

@@ -1,7 +1,7 @@
 "groups":
 - "name": "opensearch.alerts"
   "rules":
-  - "alert": "OpenSearchClusterNotHealthy"
+  - "alert": "OpenSearchClusterRed"
     "annotations":
       "message": "Cluster {{ $labels.cluster }} health status has been RED for at least 2m. Cluster does not accept writes, shards may be missing or master node hasn't been elected yet."
       "summary": "Cluster health status is RED"
@@ -10,15 +10,17 @@
     "for": "2m"
     "labels":
       "severity": "critical"
-  - "alert": "OpenSearchClusterNotHealthy"
+
+  - "alert": "OpenSearchClusterYellow"
     "annotations":
-      "message": "Cluster {{ $labels.cluster }} health status has been YELLOW for at least 20m."
+      "message": "Cluster {{ $labels.cluster }} health status has been YELLOW for at least 20m. Some cluster replicas shards are not allocated."
       "summary": "Cluster health status is YELLOW"
     "expr": |
       sum by (cluster) (opensearch_cluster_status == 1)
     "for": "20m"
     "labels":
       "severity": "warning"
+
   - "alert": "OpenSearchBulkRequestsRejectionJumps"
     "annotations":
       "message": "High Bulk Rejection Ratio at {{ $labels.node }} node in {{ $labels.cluster }} cluster. This node may not be keeping up with the indexing speed."
@@ -28,7 +30,8 @@
     "for": "10m"
     "labels":
       "severity": "warning"
-  - "alert": "OpenSearchNodeDiskWatermarkReached"
+
+  - "alert": "OpenSearchNodeDiskLowWatermarkReached"
     "annotations":
       "message": "Disk Low Watermark Reached at {{ $labels.node }} node in {{ $labels.cluster }} cluster. Shards can not be allocated to this node anymore. You should consider adding more disk to the node."
       "summary": "Disk Low Watermark Reached - disk saturation is {{ $value }}%"
@@ -44,7 +47,8 @@
     "for": "5m"
     "labels":
       "severity": "alert"
-  - "alert": "OpenSearchNodeDiskWatermarkReached"
+
+  - "alert": "OpenSearchNodeDiskHighWatermarkReached"
     "annotations":
       "message": "Disk High Watermark Reached at {{ $labels.node }} node in {{ $labels.cluster }} cluster. Some shards will be re-allocated to different nodes if possible. Make sure more disk space is added to the node or drop old indices allocated to this node."
       "summary": "Disk High Watermark Reached - disk saturation is {{ $value }}%"
@@ -60,6 +64,7 @@
     "for": "5m"
     "labels":
       "severity": "high"
+
   - "alert": "OpenSearchJVMHeapUseHigh"
     "annotations":
       "message": "JVM Heap usage on the node {{ $labels.node }} in {{ $labels.cluster }} cluster is {{ $value }}%."
@@ -69,6 +74,7 @@
     "for": "10m"
     "labels":
       "severity": "alert"
+
   - "alert": "OpenSearchHostSystemCPUHigh"
     "annotations":
       "message": "System CPU usage on the node {{ $labels.node }} in {{ $labels.cluster }} cluster is {{ $value }}%"
@@ -78,6 +84,7 @@
     "for": "1m"
     "labels":
       "severity": "alert"
+
   - "alert": "OpenSearchProcessCPUHigh"
     "annotations":
       "message": "OSE process CPU usage on the node {{ $labels.node }} in {{ $labels.cluster }} cluster is {{ $value }}%"