[Bug] program termination

[hopeyen]

Problem statement

Add graceful shutdown to the radio

Expectation proposal

The ideal process of shutting down

• First the radio stops listening to waku signals: Graphcast agent's waku node should stop
• message senders between Graphcast agent and radio operator should drop as the already received signals are processed
• All graphcast gossip operations shut down
• message processing should finish decoding, validating, and storing the messages
• radio operations should stop
• http server shuts down
• metrics shuts down
• program exits

Alternative considerations

This may fit better in the re-architecture of radios, but it is a good learning opportunity for fixing the current structure