GraphQL: Capture user-provided error extension values

[marcotc]

A follow up from #4177, this PR allows users to capture custom error fields (called extensions in GraphQL).

Here's an example of an error with extensions (link):

{
  "errors": [
    {
      "message": "Cannot query field \"__typenam\" on type \"Query\".",
      "locations": [
        {
          "line": 1,
          "column": 2
        }
      ],
      "extensions": {
        "code": "GRAPHQL_VALIDATION_FAILED",
        "stacktrace": [
          "GraphQLError: Cannot query field \"__typenam\" on type \"Query\".",
          "    at Object.Field (/my_project/node_modules/graphql/validation/rules/FieldsOnCorrectTypeRule.js:48:31)",
          "    ...additional lines..."
        ]
      }
    }
  ]
}

extensions can contain any arbitrary data, but are often important for error debugging.
Because extensions can contain PII, or pretty much any arbitrary user-provided information, the extensions that are allowed to be capture by dd-trace-rb have to be added to a list in the DD_TRACE_GRAPHQL_ERROR_EXTENSIONS configuration.

Change log entry
No. This will be covered by #4177.

How to test the change?
All changes have automated tests.

[github-actions]

Thank you for updating Change log entry section 👏

^{Visited at: 2025-01-31 22:26:52 UTC}

[datadog-datadog-prod-us1]

Datadog Report

Branch report: graphql-error-event-ext
Commit report: 8b58748
Test service: dd-trace-rb

✅ 0 Failed, 20131 Passed, 1361 Skipped, 3m 12.89s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-14 20:31:20

Comparing candidate commit 8b58748 in PR branch graphql-error-event-ext with baseline commit aa7e0da in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.70%. Comparing base (aa7e0da) to head (8b58748).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4325      +/-   ##
==========================================
- Coverage   97.71%   97.70%   -0.01%     
==========================================
  Files        1353     1355       +2     
  Lines       82975    83051      +76     
  Branches     4213     4218       +5     
==========================================
+ Hits        81078    81144      +66     
- Misses       1897     1907      +10     

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[buraizu]

Approving with a minor update requested

[Strech]

I have a minor suggestion to avoid undefined method on NilClass