Track diagnostic information on API calls

[DylanBaker]

Users and customers sometimes ask why runs are taking longer than they expect. Often, this is due to bad SQL performance, which they can analyze with the query profiler. However, sometimes it is due to API responses coming back slowly from Looker. It can be all API responses, or responses from specific endpoints.

It would be useful to be able to get diagnostics from Spectacles about how long API responses take on average and at different percentiles, both in aggregate and at the API endpoint level.