[8.0](backport #29112) x-pack/packetbeat: install Npcap at start-up when required

[mergify]

This is an automatic backport of pull request #29112 done by Mergify.
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On branch mergify/bp/8.0/pr-29112
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Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   NOTICE.txt
	modified:   dev-tools/mage/config.go
	modified:   dev-tools/mage/crossbuild.go
	modified:   dev-tools/mage/settings.go
	modified:   dev-tools/notice/NOTICE.txt.tmpl
	modified:   dev-tools/packaging/package_test.go
	modified:   packetbeat/README.md
	modified:   packetbeat/_meta/config/beat.reference.yml.tmpl
	modified:   packetbeat/_meta/config/beat.yml.tmpl
	new file:   packetbeat/_meta/config/windows_npcap.yml.tmpl
	new file:   packetbeat/beater/install_npcap.go
	modified:   packetbeat/beater/packetbeat.go
	new file:   packetbeat/npcap/npcap.go
	new file:   packetbeat/npcap/npcap_other.go
	new file:   packetbeat/npcap/npcap_test.go
	new file:   packetbeat/npcap/npcap_windows.go
	new file:   packetbeat/npcap/testdata/mock_installer.go
	new file:   packetbeat/npcap/testdata/mock_uninstaller.go
	modified:   packetbeat/scripts/mage/package.go
	new file:   x-pack/packetbeat/LICENSE-Npcap.txt
	modified:   x-pack/packetbeat/cmd/root.go
	modified:   x-pack/packetbeat/magefile.go
	new file:   x-pack/packetbeat/npcap/installer/.gitignore
	new file:   x-pack/packetbeat/npcap/installer/LICENSE
	new file:   x-pack/packetbeat/npcap/installer/README
	new file:   x-pack/packetbeat/npcap/installer/npcap-0.00.exe
	new file:   x-pack/packetbeat/npcap/npcap_other.go
	new file:   x-pack/packetbeat/npcap/npcap_windows.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   go.mod

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[elasticmachine]

💔 Build Failed

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• Start Time: 2022-01-27T05:37:11.257+0000

• Duration: 8 min 37 sec

• Commit: e1f4e41

Steps errors

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Dump mage variables

• Took 0 min 0 sec . View more details here
• Description: mage dumpVariables

Error signal

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• Description: Error 'hudson.AbortException: script returned exit code 1'

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[andrewkroh]

This should be going into 8.1 rather than 8.0, right?

[efd6]

Yes. At the start of the addition it was to be added to 8.0, but I think we missed that boat. It's merged into master, so it will be in 8.1.

[elasticmachine]

💚 Flaky test report

Tests succeeded.

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