[Core] Clear Shutdown Sequence When a Node is Gracefully Shutdown

[MengjinYan]

What happened + What you expected to happen

In the current implementation, when a node is graceful shutdown, there is no clear sequence regarding how the components are shutdown (for example, core workers should always shutdown before raylet). At the same time, in the current core worker graceful shutdown process, the raylet termination is deemed fatal and will cause core worker to directly exit without further cleanup.

Improvements need to be made to make sure clear shutdown sequence and avoid direct exit in the graceful shutdown scenario.

Versions / Dependencies

N/A

Reproduction script

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Issue Severity

None