Set additional props as tags on FunctionInvokingChatClient span

[verdie-g]

A little different than #6878 so I would prefer opening a different discussion.

When working with Langfuse, it expects the root span to have tags for the session id, user id, trace name. Today, we can pass additional props that will be set on the OTEL chat client but no on the root span of MEAI, FunctionInvokingChatClient.

Would it make sense to set additional props as tags of the FunctionInvokingChatClient span too?

[verdie-g]

The solution in #6878 also solves this one.