feat: Support Multiple System Messages with Better API

[OmCheeLin]

Description

Support Multiple System Messages with Better API. #3141

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[Wendong-Fan]

thanks @OmCheeLin 's contribution! based on previous discussion: #3113 (comment) I think we also need to update ScoreBasedContextCreator to fully support multiple system message setting

[Wendong-Fan]

seems here we are making assistant message using make_assistant_message instead of make_system_message

[hesamsheikh]

Thanks for the PR @OmCheeLin
To make the PR comprehensive, these missing parts also need to be addressed:

1. adding test cases
2. the method add_or_update_system_messages doesn't seem to implement the multiple system messages we are looking for. It must be able to create more than one system message, even in the middle of the conversation.