fix(nats sink): fix vector exiting if nats sink url fails dns resolution or is unavailable without --require-healthy

[rdwr-tomers]

Summary

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Running vector with a nats sink url pointing at an unavailable host, before the fix, results in vector exiting immediately.

For example, if the url points at a hostname that fails dns resolution the error logged is:
ERROR vector::topology::builder: Configuration error. error=Sink "nats": NATS Connect Error: DNS error: failed to lookup address information: Temporary failure in name resolution

After the fix, vector logs the same error, but continues on to try and reconnect to the NATS server. When the server becomes available, vector establishes the connection and resumes operation.

If vector is launched with --require-healthy flag it does exit on error connecting to NATS.

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Notes

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References

• Closes: #22914

[pront]

Suggested change

	Fixed crash if nats sink url is unresolvable or unavailable even when --require-healthy is not set.
	The `nats` sink now does not return an error when an unresolvable or unavailable URL is provided. Note that if `--require-healthy` is set then Vector will stop on startup.