[9.1](backport #45734) refactor: replace lopg.ObserverLogs with logptest

[mergify]

Proposed commit message

ObserverLogs is relying on a testing package in a non-test package

move to logptest

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
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• depends on Replace global loggers with local logger #13 #45720

Use cases

Screenshots

Logs

---

This is an automatic backport of pull request #45734 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of b5789af has failed:

On branch mergify/bp/9.1/pr-45734
Your branch is up to date with 'origin/9.1'.

You are currently cherry-picking commit b5789af35.
  (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:   filebeat/input/filestream/config_test.go
	modified:   heartbeat/monitors/logger/logger_test.go
	modified:   heartbeat/monitors/wrappers/wrappers_test.go
	modified:   libbeat/autodiscover/autodiscover_test.go
	modified:   libbeat/monitoring/report/log/log_test.go
	modified:   packetbeat/npcap/npcap_test.go
	modified:   x-pack/metricbeat/module/gcp/metrics/metrics_requester_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   filebeat/input/journald/pkg/journalctl/reader_test.go

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

[github-actions]

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