don't call underlying services on empty queries

[temaEmelyan]

Please make sure you consider the following:

• [ ] Add tests that use __typename in queries
• [ ] Does this change work with all nadel transformations (rename, type rename, hydration, etc)? Add tests for this.
• [ ] Is it worth using hints for this change in order to be able to enable a percentage rollout?
• [ ] Do we need to add integration tests for this change in the graphql gateway?
• [ ] Do we need a pollinator check for this?

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