[8.19](backport #47969) fbreceiver: refactor receiver tests for maintainability

[mergify]

Proposed commit message

Changes:

• Refactor TestMultipleReceivers to easily scale to n>2 receivers
• Clean up *.sock files
• Add multiReceiverHelper struct to encapsulate receiver test setup
• Add helper functions: hostFromSocket, writeFile
• Use UUID for socket path generation instead of random bytes
• Use DialContext instead of Dial to fix noctx lint warning

Pulled out from #47870 for easier review.

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. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

How to test this PR locally

Run the test

Related issues

• Blocks javascript processor: replace global paths with per-beat paths #47870

  ---

  This is an automatic backport of pull request fbreceiver: refactor receiver tests for maintainability #47969 done by Mergify.

[mergify]

Cherry-pick of 135d04f has failed:

On branch mergify/bp/8.19/pr-47969
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit 135d04f52.
  (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:   x-pack/filebeat/fbreceiver/receiver_leak_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   x-pack/filebeat/fbreceiver/receiver_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]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)