[8.x] Pluginmanager install preserve (backport #17267)

[mergify]

Release notes

[rn:skip]

What does this PR do?

Fixes a regression introduced in #17203 that caused the bin/logstash-plugin install --preserve flag to not preserve.

Why is it important/What is the impact to the user?

• When a plugin is installed with --version, the Gemfile is amended to add the plugin and its version requirement.
• When this version requirement is present, installing it again with the --preserve flag should preserve the requirement.
• A fix to allow plugins installed with --version to be upgraded had the side-effect of making the install command's --preserve not work.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

How to test this PR locally

This PR comes with tests and a fix separately. The tests can be used to verify the pre-broken behaviour as so:

1. check out the branch
2. revert the fixing commit and observe test failures:
   back-out the portion of the breaking commit

   git revert --no-commit HEAD
   ci/integration_tests.sh specs/cli/install_spec.rb
   

3. revert the portion of Pluginmanager clean after mutate #17203 that caused the regression, and observe that tests pass:

   git diff 8c969138073b98de7a99daf3c62527e5758711f9^! -- lib/pluginmanager/gemfile.rb | patch --strip 1 --reverse
   ci/integration_tests.sh specs/cli/install_spec.rb
   

---

This is an automatic backport of pull request #17267 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a736178 has failed:

On branch mergify/bp/8.x/pr-17267
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit a736178d.
  (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:   lib/pluginmanager/install.rb

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   qa/integration/specs/cli/install_spec.rb
	deleted by us:   qa/integration/specs/cli/pluginmanager_spec_helper.rb

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

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: cbbc802

Failed CI Steps

• 🥼 Integration Tests / part 2
• 🥼 Integration Tests / part 2
• 🥼 Integration Tests / part 2
• 🥼 Integration Tests / part 2
• 🥼 IT Persistent Queues / part 2
• 🥼 IT Persistent Queues / part 2
• 🥼 IT Persistent Queues / part 2
• 🥼 IT Persistent Queues / part 2

History

cc @yaauie

[donoghuc]

Closing in favor of #17270