Instrument Unicorn with Ruby exporter

What does this MR do?

Adds basic instrumentation to Unicorn based server. Using Raindrops gem we extract socket information out of socket used by Unicorn and in turn we expose those metrics using Prometheus endpoint.

In addition to socket information, we also collect request count metrics.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #33410 (closed)