Docs: Add DescribeAlarmHistory to minimal IAM policy (#23965)

DescribeAlarmHistory is used in the annotations query. 

docs/sources/features/datasources/cloudwatch.md

@@ -62,6 +62,7 @@ Here is a minimal policy example:
       "Effect": "Allow",
       "Action": [
         "cloudwatch:DescribeAlarmsForMetric",
+        "cloudwatch:DescribeAlarmHistory",
         "cloudwatch:ListMetrics",
         "cloudwatch:GetMetricStatistics",
         "cloudwatch:GetMetricData"