Track request queue time based on available request headers

[AxelTheGerman]

Hi,

I've been using the gem for a while and I added a way to parse common queue time headers.

It's been very useful to determine queue time of requests on the proxy level (before reaching the application) as it is a common source for performance issues.

Let me know if you'd be interested in accepting this change at all and I'm happy to refactor if needed.

[alexisbernard]

Thanks for taking time to write the PR. I really appreciate.

It should report the queue time with a section. Thus it is automatically displayed in the web interface :

def report_queue_time
  if queue_time = calculate_queue_time(env)
    section = Section.new
    section.stop
    section.total_ms = queue_time
    section.gc_time_ms = 0
    section.file = "request-queue"
    section.line = 0
    section.kind = "queue"
    RorVsWild.agent.add_section(section)
  end
end

[AxelTheGerman]

Thank you for the immediate response and the suggestion! I didn't know too much how sections work but that makes sense.

Will update the PR shortly :)