GraphQL CI performance improvements

What does this MR do?

This collection of improvements was implemented when working on !40088 (merged), but can be cleanly extracted here.

It includes N+1 fixes.

The changes are annotated with notes explaining the rationale.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.