[stan] Ensure event.kind is correctly set for pipeline errors

[MakoWish]

What does this PR do?

Modify stan integration to correctly set event.kind for pipeline errors and ensure error.message is an array.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

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How to test this PR locally

Related issues

• For sei: ensure packages set error.kind to "pipeline_error" in on_failure processor #6582

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• Start Time: 2023-08-10T21:42:28.603+0000

• Duration: 18 min 25 sec

Test stats 🧪

Test	Results
Failed	0
Passed	27
Skipped	0
Total	27

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚
Classes	100.0% (1/1)	💚
Methods	100.0% (20/20)	💚
Lines	95.455% (189/198)	❕
Conditionals	100.0% (0/0)	💚

[botelastic]

Hi! We just realized that we haven't looked into this PR in a while. We're sorry! We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1. Thank you for your contribution!

[botelastic]

Hi! This PR has been stale for a while and we're going to close it as part of our cleanup procedure. We appreciate your contribution and would like to apologize if we have not been able to review it, due to the current heavy load of the team. Feel free to re-open this PR if you think it should stay open and is worth rebasing. Thank you for your contribution!