tech debt listing

[RobinQu]

This is a long running issue that tracks technical debts found in existing code base.

• [ ] transaction management in instinct-assistant services.
• [ ] ProtobufUtils refactoring #29
• [ ] RE2, ICU, or both?
• [ ] protobuf genearted classes are not header-only #29
• [ ] improving json context access #29
• [ ] stream api support #28