Request/Response body size metric per operation name

[grzn]

The metric 'apollo_router_http_request_duration_seconds' is great, exposing the duration for each Gql operation. It would even better to have a metric for the request/response body sizes per opeation.

From what I gather this is not doable with a custom router metric (does not have the operation name selector/attribute) and not with a super graph selector/attribute (does not have the request/body size)