Limit number of GraphQL requests tracked in performance bar to 10

What does this MR do?

Previously, we only tracked up to 2 requests to the same URL in the performance bar. For GraphQL, we removed that limit as the URL is the same for all GraphQL requests, and we didn't want to miss anything that was genuinely new.

However, with no limit, if we poll using GraphQL then we'll end up with this store increasing forever. So we set a higher - but still reasonable - limit of 10 GraphQL requests to be stored in the performance bar. Other requests can still be added manually by request ID as normal.

For #327214 (closed).