feat: Implement a shutdown signal listener function

[gengteng]

Hi,

In this PR, I've tackled two TODO items related to our server's signal handling for shutdown and upgrade processes:

1. Centralized Signal Listening: Introduced a function to listen for shutdown signals, streamlining previous scattered logic.
2. Enhanced Graceful Upgrades: Ensured rapid shutdown signals are considered during upgrades, bolstering the process's reliability.

These changes aim to clarify and refine our approach, potentially aligning with the original design intentions. I'm curious to hear if this matches our design goals or if there's a preferred direction.

Thanks.