Use endpoint_url if provided with boto3 session for dynamodb (#11622)

- **Description:** Uses `endpoint_url` if provided with a boto3 session.
When running dynamodb locally, credentials are required even if invalid.
With this change, it will be possible to pass a boto3 session with
credentials and specify an endpoint_url

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>
Co-authored-by: Erick Friis <erick@langchain.dev>

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

@@ -53,7 +53,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         kms_key_id: Optional[str] = None,
     ):
         if boto3_session:
-            client = boto3_session.resource("dynamodb")
+            client = boto3_session.resource("dynamodb", endpoint_url=endpoint_url)
         else:
             try:
                 import boto3