Revert "add errors for response validation (#5787)"

[goto-bus-stop]

This reverts commit 39c6c03.

#5787 contained a bug that reported a GraphQL field error when a subgraph replied with null for an enum field, even if that field is declared as nullable. While that is easy to address, we found in #6313 that many of our tests were not properly checking for error cases, so the work became a bit more sprawling and not able to be completed for 1.58.0.

After finding this bug, we are also not as confident on the change as a whole, and if it breaks, the way it breaks is very bad. Hence the choice to revert it out of 1.58.0.

To land this again, I believe we need stronger testing, including all possible permutations of nullable/non-nullable, list/non-list fields, and all permutations of GraphQL and JSON types. Additionally, we may need to put the new error handling in router 2.0 only. I think we should land the tests in both 1.x and 2.0, to nail down the current behaviour.

#5787 also contained minor fixes to existing error messages. We can reintroduce those fixes in 1.x along with the expanded tests.

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Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

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Notes

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1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

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3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

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[router-perf]

CI performance tests

• connectors-const - Connectors stress test that runs with a constant number of users
• const - Basic stress test that runs with a constant number of users
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• enhanced-signature - Enhanced signature enabled
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• extended-reference-mode - Extended reference mode enabled
• large-request - Stress test with a 1 MB request payload
• no-tracing - Basic stress test, no tracing
• reload - Reload test over a long period of time at a constant rate of users
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• step-local-metrics - Field stats that are generated from the router rather than FTV1
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• xxlarge-request - Stress test with 100 MB request payload

[goto-bus-stop]

One new test is failing because the revert reintroduces a bug in the error message that we report. I'll update that test to expect the wrong thing, as it's not critical