fix(processors.parser): Handle metrics without inner timestamp correctly

[srebhan]

Summary

This PR uses the newly introduced ParserTimeFuncPlugin plugin interface to make sure the inner parser returns a zero timestamp in cases where the data-to-parse does not provide time information.

Checklist

• No AI generated code was used in this PR
• AI generated code used in this PR follows the InfluxData Policy on AI-Generated Code Contributions

Related issues

resolves #16331

[skartikey]

@srebhan Looks good, The only remaining part is updating the README. The override-with-timestamp description still reads "override the timestamp with the one of the latest parsed metric," with no "if it exists" caveat.

[skartikey]

@srebhan Thanks!

[telegraf-tiger]

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amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
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i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
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ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
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s390x.deb		linux_i386.tar.gz
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