[7.17] Add license (backport #5360)

[mergify]

Relates to elastic/docs#2396

This PR adds the https://creativecommons.org/licenses/by-nc-nd/4.0/ license.
It also updates the readme per https://github.com/santisoler/cc-licenses?tab=readme-ov-file#cc-attribution-noncommercial-noderivs-40-international

---

This is an automatic backport of pull request #5360 done by Mergify.

[mergify]

Cherry-pick of 70d952f has failed:

On branch mergify/bp/7.17/pr-5360
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit 70d952f1.
  (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:
	new file:   LICENSE

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

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

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