Projects::MergeRequestsController#bulk_update P90 is above 500ms

According to this Kibana visualization, the Projects::MergeRequestsController#bulk_update action has a P90 of 3.279s (above our 500ms target) for that last 7 days as of this writing (2021-03-24). It doesn't have a lot of requests though.

Looking at this grafana dashboard, it shows that SQL requests per request can get up to 2k.