chore: Fix linter findings for revive:enforce-slice-style in plugins/parsers, plugins/processors, plugins/secretstores and plugins/serializers

[zak-pawel]

Summary

Address findings for revive:enforce-slice-style in plugins/parsers, plugins/processors, plugins/secretstores and plugins/serializers.

As we agreed here #15812, we will fix the errors found by the following configuration:

      - name: enforce-slice-style
        arguments: ["make"]

It is only part of the bigger job.
After all findings of this type in whole project are handled, we can enable revive:enforce-slice-style rule in golangci-lint.

Checklist

• No AI generated code was used in this PR

[srebhan]

Thanks for the PR. I wonder if you can leave out all the make([]xyz, 0) statements in the tests to simplify the code!?

[srebhan]

There are some more instances that can be removed IMO...

[srebhan]

Just one last suggestion @zak-pawel! ;-)

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_arm64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
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
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz

[srebhan]

Thanks a lot @zak-pawel!