DynamoDBChatMessageHistory does not handle GSI keys.

[mlnrt]

Hello,
The documentation and code of DynamoDBChatMessageHistory, mentions that the "key" parameter can include both the composite key DynamoDB GSI LSI keys.
Reference: "This may also contain global and local secondary index keys"
But this doesn't work since the add_messages method simply expands the key parameter and passes everything into the key. But according to the boto3 update_item() documentation, the Key parameter can only include the primary and search key.
However, the ability to add additional attributes and GSI/LSI would definitely be a plus.
I might be able to help on this with instructions on how to participate.