fix: Add validation for incompatible Datadog and trace context propagation

[abernix]

Prevents simultaneous activation of Datadog tracing and W3C trace context propagation to avoid trace ID format conflicts.

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Checklist

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

• [x] PR description explains the motivation for the change and relevant context for reviewing
• [x] PR description links appropriate GitHub/Jira tickets (creating when necessary)
• [x] Changeset is included for user-facing changes
• [x] Changes are compatible[^1]
• [x] Documentation[^2] completed
• [x] Performance impact assessed and acceptable
• [x] Metrics and logs are added[^3] and documented
• Tests added and passing[^4]
  • [x] Unit tests
  • [x] Integration tests, as necessary
  • [x] Manual tests, as necessary

Exceptions

Note any exceptions here

Notes

[^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. [^2]: Configuration is an important part of many changes. Where applicable please try to document configuration examples. [^3]: A lot of (if not most) features benefit from built-in observability and debug-level logs. Please read this guidance on metrics best-practices. [^4]: Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions.

[apollo-librarian[bot]]

✅ Docs preview ready

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File Changes

0 new, 3 changed, 0 removed

* graphos/routing/(latest)/observability/telemetry/trace-exporters/overview.mdx
* graphos/routing/(latest)/operations/subscriptions/configuration.mdx
* graphos/routing/(latest)/performance/caching/entity.mdx

Build ID: 19c91de500bbbf2acecf585d

URL: https://www.apollographql.com/docs/deploy-preview/19c91de500bbbf2acecf585d

[abernix]

Putting this back to draft, because many of the integration tests need some work before they'll pass.

[BrynCooke]

I'm taking this over