feat(chat): change `ChatHistorySerializer` to fit API requirements
feat(chat): change `ChatHistorySerializer` to fit API requirements

Chages:
- delete `HistoryMessage` serializer

raccoongang/socraticqs2,raccoongang/socraticqs2,raccoongang/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2