Don't dynamically add mappings for Kibana meta to avoid field explosion

[rudolf]

Fixes #45255

Proposed commit message

The meta field in Kibana logs contains additional metadata that might be useful for understanding a log entry. This often means meta is a deeply nested object, mapping every field in this object causes a mapping explosion and slows down the Kibana UI. Users should not have to filter or search on the meta 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
• I have added tests that prove my fix is effective or that my feature works. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

Disruptive User Impact

Users should not be relying on the meta field or any keys therein.

Author's Checklist

• [ ]

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[github-actions]

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[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @rudolf? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[consulthys]

LGT Stack Monitoring