server: add request metrics about go-cloud

[zombiezen]

@clausti, are you still working on this issue? It might be a good one for @jba to take since he's working on metrics.

[clausti]

I have not worked on this, no. I don't mind if someone else takes it.

[Tazer]

When looking around a little there seem to be a http plugin for open census ochttp
https://github.com/census-instrumentation/opencensus-go/blob/master/examples/http/helloworld_server/main.go#L89

Not sure if it even would be a possibility to use that plugin? Anyway they have some defined standard metrics

Server:
https://github.com/census-instrumentation/opencensus-go/blob/master/plugin/ochttp/stats.go#L226
Client:
https://github.com/census-instrumentation/opencensus-go/blob/master/plugin/ochttp/stats.go#L137

[jba]

You should use that plugin. See https://code.googlesource.com/google-api-go-client/+/refs/heads/master/transport/http/dial.go.