Instrument db calls for sidekiq and reqest

What does this MR do?

This MR adds the following metrics for lograge and for structured_logger (sidekiq logs):

• db_count for all SELECTs?
• db_write_count as they create a sticky connection, all that is not SELECT?
• db_cached_count: they are still expensive on Rails side to instantiate the objects

I added those metrics in lograge for puma/unicorn and for sidekiq in structured-logger

I also introduced Prometheus metrics:

• db_count
• db_write_count
• db_cached_count

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #216835 (closed) Related to #217103 (closed)