Log cpu user time to structured logging

As part of the ongoing effort to discover CPU intensive endpoints #30567 (closed) to aid in PUMA rollout, in this MR we are logging cpu_s to structured logging.

As discussed in #31887 (closed) we would need getrusage(RUSAGE_THREAD) and till #31891 (closed) is resolved we can get user_s alone using

Process.clock_gettime(Process::CLOCK_THREAD_CPUTIME_ID)

Also to note:

We are using Lograge and it logs at the end of the controller and the time spent in the middleware after the controller is not captured. We acknowledge the limitations of Lograge and will fix it in a separate issue as discussed in gitlab-foss!31942 (comment 217619089)

This MR closes #30567 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content