Update CloudWatch plugin's required IAM permissions (#1566)

Signed-off-by: Adis Osmonov <[email protected]>

Author: adis-io

pipeline/outputs/cloudwatch.md

@@ -137,7 +137,8 @@ The following AWS IAM permissions are required to use this plugin:
     "Action": [
       "logs:CreateLogStream",
       "logs:CreateLogGroup",
-      "logs:PutLogEvents"
+      "logs:PutLogEvents",
+      "logs:PutRetentionPolicy"
     ],
     "Resource": "*"
   }]