Add information about CloudFormation status on AWS

After removing `logstashstack`, there are still several other stacks currently
running on AWS. While one of them may not be easily removable,
so it is worth to mention that information in the README file.

Change-Id: I82e879291037255816b2ee1197ebc79065d5d143

opensearch-config/README.md

@@ -4,6 +4,18 @@
 
 This folder contains CloudFormation configurations for an AWS OpenSearch cluster and a set of Logstash servers behind a load balancer.
 
+## Deprecation Notice
+
+This file contains historical configurations related to the deployment of the OpenSearch service on AWS.
+The logstash service (deployed by logstashstack) is no longer used by the OpenDev community and it has been replaced by the logsender tool.
+
+The current AWS CloudFormation configuration includes:
+
+- `opensearchstack` - for OpenSearch
+- `ecr-stack` - storing admin credentials for OpenSearch in Secret Manager.
+
+Note: The `ecr-stack` may be removed in the future, but doing so requires changing administrator credentials!
+
 ## Usage
 
 You'll need appropriate AWS permissions (to create and monitor resources). Put AWS credentials in `~/.aws/credentials` and run `deploy_opensearch.sh`.
@@ -17,7 +29,7 @@ The Opensearch service requires additional configuration like creating readonly
 Users will be created in the Opensearch dashboards service.
 We create only few internal users:
 
-* logstash - that will be used by logstash or logsender service
+* logstash - that will be used by logstash or logsender service (deprecated; replaced by logsender)
 * readonly - readonly user that will be able to discover data, check visualization and dashboards
 * openstack - readonly user with easy to remember password
 
@@ -51,7 +63,7 @@ tenant permissions:
   tenant: global_tenant
 ```
 
-* Logstash role (modify)
+* Logstash role (modify) - deprecated
 Details:
 
 ```