chat API does not support user-defined conversation id

[cyflhn]

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Dify version

0.13.2

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

1. call API of /v1/chat-messages with parameter of "conversation_id" which is not returned by previous API call

✔️ Expected Behavior

get a normal response

❌ Actual Behavior

if the response will be "conversation not exists"