Possible memory leak in ApolloServerPluginUsageReporting
Package: apollo-server-core@^3.10.2

We are running a federated gateway with an instance of the ApolloServerPluginUsageReporting. Over time we are seeing heap memory of these servers steadily increasing. As of 30 Sept we changed the `fieldLevelInstrumentation` option passed to the plugin from the default 100% down to 10%. This has seen a decrease in the amount of memory being used by our federated gateway however it is continuing to increase over time.

I believe there is an issue with the `getReportData` function used internally within the usage reporting plugin 

https://github.com/apollographql/apollo-server/blob/0e42833409236ce91f2d2bd90f3db8f2d2765eec/packages/apollo-server-core/src/plugin/usageReporting/plugin.ts#L196

The function appears to be storing ReportData objects in a plain object `Record<string, ReportData>` but does not seem to ever remove entries from this object. I would expect these entries to be removed once the reports have been sent to Apollo Studio.

Apologies for the lack of a repro case, I have not been able to pull something together that is able to replicate what we are seeing in our production environments

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