chore: Create client API conversations with custom attributes (#8040)

- Update client API create conversations endpoint to accept custom attributes as well.

swagger/definitions/index.yml

@@ -138,6 +138,9 @@ public_message_create_payload:
 public_message_update_payload:
   $ref: ./request/public/message/update_payload.yml
 
+public_conversation_create_payload:
+  $ref: ./request/public/conversation/create_payload.yml
+
 ##  ---------- RESPONSE ------------- ##
 ## -------------------------------- ##
 

swagger/definitions/request/public/conversation/create_payload.yml

@@ -0,0 +1,5 @@
+type: object
+properties:
+  custom_attributes:
+    type: object
+    description: Custom attributes of the conversation