chore: Fix linter findings for revive:max-public-structs in plugins/inputs/[a-n]*

[zak-pawel]

Summary

Address following findings for revive:max-public-structs in plugins/inputs/[a-g]*:

plugins/inputs/activemq/activemq.go:2:1                                revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/ctrlx_datalayer/ctrlx_datalayer_subscription.go:1:1     revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/dcos/client.go:1:1                                      revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/graylog/graylog.go:2:1                                  revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/kafka_consumer/kafka_consumer.go:2:1                    revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/kubernetes/kubernetes_metrics.go:1:1                    revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/logstash/logstash.go:2:1                                revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/mailchimp/chimp_api.go:1:1                              revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/mongodb/mongostat.go:8:1                                revive  max-public-structs: you have exceeded the maximum number of public struct declarations
plugins/inputs/monit/monit.go:2:1                                      revive  max-public-structs: you have exceeded the maximum number of public struct declarations

As proposed here #15822, we will fix the errors found by the following configuration:

      - name: max-public-structs
        exclude: ["TEST"]
        arguments: [5]

  # Excluding configuration per-path, per-linter, per-text and per-source
  exclude-rules:
    - path-except: ^plugins/(aggregators|inputs|outputs|parsers|processors|serializers)/...
      text: "max-public-structs: you have exceeded the maximum number of public struct declarations"

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

Checklist

• No AI generated code was used in this PR

[srebhan]

Thanks @zak-pawel! Just two small comments while we are at it. I also realized that we can probably remove some non-content comments on structs but this is optional...

[telegraf-tiger]

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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 @zak-pawel!