(EAI-566): Support creating new conversation when add message when conversationId = "null"

docs/docs/server/openapi.yaml

@@ -39,7 +39,13 @@ paths:
     post:
       operationId: addMessage
       summary: Add message to the conversation
-      description: Add a message to the conversation and get a response back from chatbot.
+      description: |
+        Add a message to the conversation and get a response back from chatbot.
+
+        You can configure your server to create new conversations
+        when you set the conversation ID to `null`.
+        If you do this, the server creates a new conversation
+        and returns the conversation ID in the response's `metadata.conversationId` field.
       parameters:
         - $ref: "#/components/parameters/conversationId"
         - name: stream
@@ -218,13 +224,17 @@ components:
       type: object
       required:
         - id
+        - conversationId
         - role
         - content
         - createdAt
       properties:
         id:
           type: string
           description: The unique identifier for a message.
+        conversationId:
+          type: string
+          description: The unique identifier for a conversation.
         role:
           type: string
           enum: [user, assistant]