Update metric names to match Prometheus guidelines.

What does this MR do?

Updates metric names to follow upstream guidelines0.

• Simplify metrics by adding response lables to the histogram.
• Use standard http_request_duration_seconds_... names for the histogram.
• Add _total to counters.
• Add seconds unit to latency metrics.
• Update metrics documentation.

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?

• Documentation created/updated
• 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 #35031 (closed)