in_kubernetes_filter: add namespace_metadata_only option to fix regression from #8279

[ryanohnemus]

fix regression in 3.0 from #8279

fixes #8642

Adds a new namespace_metadata_only config option that is off by default. When this option is enabled it allows you to fetch only namespace metadata without also having to fetch pod metadata.

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Testing
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• Example configuration file for the change
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Documentation

• Documentation required for this feature

fluent/fluent-bit-docs#1352

Backporting

• Backport to latest stable release.

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[ryanohnemus]

@edsiper this should be ready to go, I did a few different configuration tests and they should hopefully resolve the regression. Can we add the safe for CI test flags to this one? That should give us an extra check now that there are some kubernetes plugin CI tests added :)

[edsiper]

thanks for working on this in a timely manner, I will go ahead and merge it now, definitely we need to think how to test this in our CI (any idea is welcome)

[edsiper]

FYI: changing the commit prefix to filter_kubernetes: ...