multi: manage shutdown requests with status codes

[mohamedawnallah]

Change Description

In this commit, we handle shutdown requests with status codes:

• Code 1: Critical errors (e.g., failed chain backend connection).
• Code 0: Normal shutdowns (e.g., Stop Daemon RPC).

Replaces #8659 Closes #5625

Additional Context

Shutdown Scenario	Status Code	Description
Critical Error (e.g., exhausted attempts connecting to chain backend)	1	Indicates a failure that requires immediate attention and prevents normal operation of the daemon.
Normal Shutdown (e.g., Stop Daemon RPC call)	0	Represents a graceful termination initiated by the user or a normal process shutdown.

Credits

• @ellemouton: Provided a simpler design for the issue.
• @Chinwendu20: Highlighted that the initial draft of PR #8659 was over-engineered.

Steps to Test

Steps for reviewers to follow to test the change.

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• [ ] Tests covering the positive and negative (error paths) are included.
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[Abdulkbk]

Hi @mohamedawnallah, thank you for the PR. I wanted to test it before reviewing the code, but I noticed the steps for testing were not included. I did follow the instructions you provided here, but I found them to be a bit unclear. For example, could you clarify what you mean by (or provide an example):

Make sure you have configured chain backend health checks in the lnd.conf or you could pass it through lncli.

I attempted to make LND fail by stopping BTCD (using BTCD instead of bitcoind), as you mentioned in steps 3 and 4. However, LND keeps retrying to connect for an extended period. This might be because I misunderstood the previous steps you highlighted.

I was finally able to crash LND by corrupting my wallet.db file and executing lncli listchaintxns, the node crashed but checking for the status code with echo $? returns "2" (which isn't 1 or 0). Is the status code only applicable to a specific set of error causes?.

Finally, kindly rebase so I can take a look at the code. Cheers!

[mohamedawnallah]

Thank you very much for taking a closer look at my PR, @Abdulkbk. It appears there are some cases that haven't been handled yet. I'll take a look at this PR soon 🙏