Request Trace

[xzhaosg]

What would you like to be added:
User can optionally turn on the request Trace. When it is turned on, it will record the following information of the request:

{ request_id: xxx, request_timestamp: xxx, response_timestamp: xxx, input_length: 123, output_length: 456, queued_time: 10, type: text | image | audio, ... }
Why is this needed:
The trace file will be useful for two purposes:

1. Troubleshooting any performance related issue with EPP.
2. Trace file can be used to replay the same traffic pattern for benchmarking purpose.

[ahg-g]

We added x-request-id to #746; are you suggesting to log this into a separate file as a trace?

@danehans @robscott how do proxies typically offer features like this?

[xzhaosg]

Request Id is not sufficient, we need additional information such as input token length and output token length. if it is easy to filter trace data from a log, then a separate logging is not needed but we should make it easy to turn on the trace without additional overhead.