[8.x](backport #41571) Add debug logging statements to auditbeat system/socket metricset

[mergify[bot]]

Proposed commit message

This seems a little needless, but last time I had to fix the system/socket module it took forever. The code is old, complicated, and few people seem to actually understand it. This adds a handful of debug-level statements to the control flow, so if/when we run into problems with this again, we can tell someone to enable debug logging, and hopefully shorten the debugging process.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] 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.

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  This is an automatic backport of pull request #41571 done by Mergify.

[botelastic[bot]]

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