apollo-server-core: Improve a usage reporting misuse error

This error generally should arise when people try to use the unexported AS 1.x
API instead of the 2.x API. (If we find other cases that trigger this error we
can update the linked issue.)

Fixes #4588.

packages/apollo-server-core/src/plugin/usageReporting/plugin.ts

@@ -77,6 +77,13 @@ export function ApolloServerPluginUsageReporting<TContext>(
     // this little hack. (Perhaps we should also allow GraphQLServerListener to contain
     // a requestDidStart?)
     requestDidStart(requestContext: GraphQLRequestContext<TContext>) {
+      if (!requestDidStartHandler) {
+        throw Error(
+          'The usage reporting plugin has been asked to handle a request before the ' +
+            'server has started. See https://github.com/apollographql/apollo-server/issues/4588 ' +
+            'for more details.',
+        );
+      }
       return requestDidStartHandler(requestContext);
     },