Remove warn option of event_api.tags.illegal

[kaisecheng]

_Do Not Merge until we got approval from breaking changes committee _

Release notes

Removed the --event_api.tags.illegal warn option, which allowed setting non string values to the tags field. Since v9, such assignments will fail, resulting in a _tagsparsefailure in the tags field, and the illegal value will be written to the _tags field.

What does this PR do?

The commit removes the --event_api.tags.illegal warn option which is added in #14822

Why is it important/What is the impact to the user?

This is a breaking change. User no longer be able to set event_api.tags.illegal to warn as a fallback to accept the illegal assignment of tags field.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• run with --event_api.tags.illegal warn throws Invalid option
• --event_api.tags.illegal rename work as expected

How to test this PR locally

Related issues

• Fixes: Remove event_api.tags.illegal (default becomes locked to 'rename') #16356

Use cases

Screenshots

Logs

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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