[docs] Add AWS Auth OpenSearch (#304)

Author: damgouj

docs/deployment/assets/backend_role.png

@@ -104,13 +104,36 @@ Each OpenCTI connection is scoped to an OpenAEV tenant, identified by its UUID (
 
 #### Engine
 
+2 options are available for the engine: 
+
+- With a classic authentication, you can use either ElasticSearch or OpenSearch as an engine.
+
 | Parameter              | Environment variable   | Default value         | Description                                                                                    |
 |:-----------------------|:-----------------------|:----------------------|:-----------------------------------------------------------------------------------------------|
-| engine.engine-aws-mode | ENGINE_ENGINE_AWS_MODE | no                    | Whether to use AWS SigV4 authentication (yes or no)                                            |
+| engine.engine-aws-mode | ENGINE_ENGINE_AWS_MODE | no                    | Classic authentication (no)                                                                    |
 | engine.engine-selector | ENGINE_ENGINE_SELECTOR | elk                   | Engine to use for storage and search (`elk` for ElasticSearch and `opensearch` for OpenSearch) |
 | engine.url             | ENGINE_URL             | http://localhost:9200 | URL of the ElasticSearch database                                                              |
 | engine.username        | ENGINE_USERNAME        |                       | This parameter is optional. Login for the database                                             |
-| engine.password        | ENGINE_PASSWORD        |                       | This parameter is optional. Password for the database                                               |
+| engine.password        | ENGINE_PASSWORD        |                       | This parameter is optional. Password for the database                                          |
+
+- With AWS SigV4 authentication, you can use Amazon OpenSearch or Amazon OpenSearch Serverless as an engine.
+
+| Parameter                | Environment variable     | Default value         | Description                                                                                                |
+|:-------------------------|:-------------------------|:----------------------|:-----------------------------------------------------------------------------------------------------------|
+| engine.engine-aws-mode   | ENGINE_ENGINE_AWS_MODE   |                       | Whether to use AWS SigV4 authentication Amazon OpenSearch or Amazon OpenSearch Serverless (`es` or `aoss`) |
+| engine.engine-selector   | ENGINE_ENGINE_SELECTOR   |                       | Engine to use for storage and search (`opensearch` for OpenSearch)                                         |
+| engine.engine-aws-host   | ENGINE_ENGINE_AWS_HOST   |                       | URL of the OpenSearch database, no http(s) prefix                                                          |
+| engine.engine-aws-region | ENGINE_ENGINE_AWS_REGION |                       | Example: eu-west-3                                                                                         |
+
+!!! tip "Adding the needed authorization to AWS OpenSearch"
+
+    * Connect to your AWS opensearch dashboard
+    * Navigate to Security, Role
+    * Click on “all_access” role, and “Mapped users” tab
+    * Add as Backend role the IAM role for your EKS node
+    * ![Backend role mapping in AWS OpenSearch](assets/backend_role.png)
+    
+    
 
 If you switch your engine selector, you'll need to delete the `indexing_status` table in PostgreSQL to trigger a full
 reindex.