Add support for scoping GraphQL to organizations

Background

We need a way to scope GraphQL queries to an organization. See https://docs.gitlab.com/ee/architecture/blueprints/cells/impacted_features/graphql.html#31-graphql-routable-by-endpoint for a few options

Proposal

Anonymous requests go to the Default Organization.

Other requests route to their corresponding Organization.

Implementation plan

Needs refinement after agreeing on proposal