In `AgentServer`, each task type needs to be processed separately,
which leads to very long code, hard to read, and not easy to detect
errors (for example, some task type processing may be missed,
corresponding relationship may be error)
Fortunately, the code for each task_type is very similar, so this
is a good case to use `MACRO`, which can greatly reduce the repeated
code and solve above problems.
This patch also fix two small bugs:
1. The `_topic_subscriber` member has not been released in dtor
2. in `submit_tasks()`, the `status_code` is not reset before
each task is processed, resulting in wrong judgment.
No functional changes in this patch.
e991b1300f