Separate GraphQL Grafana dashboard

Currently, the only view onto GraphQL we have in Grafana is the api: Rails Controller dashboard. This aggregates over all GraphQL queries.

We should probably have more fine-grained views for this, since the characteristics for different queries could be very different.

Proposal

Add a dashboard that will be placeholder for GraphQL-related panels. Start with a single text panel describing what the dashboard is used for, reference the GraphQL API observability blueprint.

Add a second panel with GraphQL controller / execute action request rate per second.