useChat: add a clearError handler

[alvarosevilla95]

Feature Description

Be able to clear the error from useChat without calling reload or handleSubmit

Use Cases

I have a button to clear the chat window (which calls setMessages([])). However, if there was an error in the conversation, the error persists after clearing the messages. I'd like to be able to clear the error when I call my chatClear function, so the chat gets reset to a default state.

I can currently get around this by adding messages.length > 0 && error to display the error, but it would be cleaner if I could just clear it.

Additional context

No response