Top10 expensive fields in GraphQL 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

Add a panel with top 10 most expensive GraphQL fields, similarly to top PostgreSQL queries dashboard:

postresql_top_queries

/cc @pslaughter @dsatcher @deuley