Reassess contexts in subsystems, revise cancellation, setup graceful shutdown

## Issue Summary
- As a continuation from this [comment](https://github.com/ChainSafe/gossamer/pull/3837#discussion_r1578211273), we should reassess contexts in subsystems and establish a good pattern for closing of channels and to implement graceful shutdown for subsystems.
- Implement changes for all existing subsystem work
- Overseer should shutdown gracefully if all subsystems have closed
- We discussed the service pattern a little in this [discussion](https://github.com/ChainSafe/gossamer/discussions/2293).