Add histograms to top10 GraphQL fields dashboard
Description
We want to build a separate GraphQL Grafana dashboard, see #583 (moved).
See GraphQL API Observability architectural blueprint https://docs.gitlab.com/ee/architecture/blueprints/graphql_api/.
Proposal
This is a follow-up issue after #981 (moved) is done. We would like to add histograms to the panel with top 10 most expensive GraphQL fields, so that it is clear what does it take to process the most expensive fields.