Usage reporting: add error stats

[BrynCooke]

There's a couple fields in our reports.proto that we are not populating right now that would help power the https://studio.apollographql.com/graph/{GRAPH_ID}/operations?tab=errors&variant={VARIANT} page that we would be good to add to the Router. These include:

• root_error_stats
• requests_with_errors_count

Needs to be investigated

• We should look at how Apollo Server and Apollo Gateway capture this information.

[abernix]

@jsegaran @sachindshinde Are we correct in understanding the purpose of these fields and their importance?

[abernix]

Relates to #74

[abernix]

We do now capture this information and this was accomplished as part of #74. We do not yet populate Error itself, but that will be tracked in another issue.