Bump elastic stack version automation (backport #25148)

[mergify]

This is an automatic backport of pull request #25148 done by Mergify.

Cherry-pick of cc29196 has failed:

On branch mergify/bp/7.x/pr-25148
Your branch is up to date with 'origin/7.x'.

You are currently cherry-picking commit cc29196dfb.
  (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:   .ci/bump-stack-version.sh
	modified:   .gitignore

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .mergify.yml

To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

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[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: Pull request #25282 opened

• Start Time: 2021-04-23T16:13:46.565+0000

• Duration: 17 min 12 sec

• Commit: 58b8815

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