[Feat] Add optional client-side encryption to DynamoDB chat history memory (#11115)

**Description:** Added optional client-side encryption to the Amazon
DynamoDB chat history memory with an AWS KMS Key ID using the [AWS
Database Encryption SDK for
Python](https://docs.aws.amazon.com/database-encryption-sdk/latest/devguide/python.html)
**Issue:** #7886
**Dependencies:**
[dynamodb-encryption-sdk](https://pypi.org/project/dynamodb-encryption-sdk/)
**Tag maintainer:**  @hwchase17 
**Twitter handle:** [@jplock](https://twitter.com/jplock/)

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/langchain/langchain/memory/chat_message_histories/dynamodb.py

@@ -38,6 +38,8 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
             This argument is optional, but useful when using composite dynamodb keys, or
             isolating records based off of application details such as a user id.
             This may also contain global and local secondary index keys.
+        kms_key_id: an optional AWS KMS Key ID, AWS KMS Key ARN, or AWS KMS Alias for
+            client-side encryption
     """
 
     def __init__(
@@ -48,6 +50,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         primary_key_name: str = "SessionId",
         key: Optional[Dict[str, str]] = None,
         boto3_session: Optional[Session] = None,
+        kms_key_id: Optional[str] = None,
     ):
         if boto3_session:
             client = boto3_session.resource("dynamodb")
@@ -66,6 +69,32 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         self.session_id = session_id
         self.key: Dict = key or {primary_key_name: session_id}
 
+        if kms_key_id:
+            try:
+                from dynamodb_encryption_sdk.encrypted.table import EncryptedTable
+                from dynamodb_encryption_sdk.identifiers import CryptoAction
+                from dynamodb_encryption_sdk.material_providers.aws_kms import (
+                    AwsKmsCryptographicMaterialsProvider,
+                )
+                from dynamodb_encryption_sdk.structures import AttributeActions
+            except ImportError as e:
+                raise ImportError(
+                    "Unable to import dynamodb_encryption_sdk, please install with "
+                    "`pip install dynamodb-encryption-sdk`."
+                ) from e
+
+            actions = AttributeActions(
+                default_action=CryptoAction.DO_NOTHING,
+                attribute_actions={"History": CryptoAction.ENCRYPT_AND_SIGN},
+            )
+            aws_kms_cmp = AwsKmsCryptographicMaterialsProvider(key_id=kms_key_id)
+            self.table = EncryptedTable(
+                table=self.table,
+                materials_provider=aws_kms_cmp,
+                attribute_actions=actions,
+                auto_refresh_table_indexes=False,
+            )
+
     @property
     def messages(self) -> List[BaseMessage]:  # type: ignore
         """Retrieve the messages from DynamoDB"""