No spec for HTTP specific metrics

[gfuller1]

Problem: There's no standard around what metric instruments to use or what labels to use for capturing HTTP activity. This can lead to problems when trying to navigate the data or filter it.

Example: one instrumented framework captures HTTP information and reports a metric for its duration as http.duration and include a label for the response code response_code. Another instrumented framework captures HTTP information and reports a metric for its duration as http.client.request.duration and includes a label for the response code but it is status_code. When someone tries to filter their data for HTTP metrics they will have a poor experience due to the inconsistencies in the data.

Solution: Write a spec to describe how to create HTTP metrics.

[tigrannajaryan]

After merging #739 there are now conventions for HTTP metrics. Do we need something else in addition in the spec?

[jmacd]

I think nothing else is needed here.