[8.0](backport #28786) licenses: Add Elastic License 2.0 (Elasticv2)

[mergify]

This is an automatic backport of pull request #28786 done by Mergify.
Cherry-pick of 8556093 has failed:

On branch mergify/bp/8.0/pr-28786
Your branch is up to date with 'origin/8.0'.

You are currently cherry-picking commit 855609362.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   NOTICE.txt
	modified:   dev-tools/cmd/license/license_generate.go
	modified:   dev-tools/mage/fmt.go
	new file:   licenses/ELASTIC-LICENSE-2.0-header.txt
	new file:   licenses/ELASTIC-LICENSE-2.0.txt
	modified:   licenses/license_header.go

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

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]

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• Start Time: 2021-11-05T01:39:03.818+0000

• Duration: 198 min 7 sec

• Commit: 1024fa6

Test stats 🧪

Test	Results
Failed	0
Passed	53998
Skipped	5355
Total	59353

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