Log errors from v2 client errors channel

[blakerouse]

What does this PR do?

Adds go-routine that reads errors from the Errors() channel and logs them.

Why is it important?

Without this its possible that the elastic-agent-client will block if errors are not pulled off the Errors() channel. Errors communicating with the Elastic Agent are also not reported.

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.

Related issues

• Closes The Beat agent control protocol client does not drain the Errors channel #34381

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[elasticmachine]

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Build stats

• Start Time: 2023-01-26T14:59:00.252+0000

• Duration: 60 min 34 sec

Test stats 🧪

Test	Results
Failed	0
Passed	7443
Skipped	343
Total	7786

💚 Flaky test report

Tests succeeded.

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b fix-34381 upstream/fix-34381
git merge upstream/main
git push upstream fix-34381