Support span_attributes testing in datadog and OTLP exporters (backport #7369)

[carodewig]

This backport enables testing of span attributes in the datadog and OTLP exporters. It does not backport any of the core functionality of #7369, which changed how some attributes were passed through the telemetry codebase.

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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

Exceptions

Note any exceptions here

Notes

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This is an automatic backport of pull request #7369 done by [Mergify](https://mergify.com).

Footnotes

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

[mergify]

Cherry-pick of 47925d0 has failed:

On branch mergify/bp/1.x/pr-7369
Your branch is up to date with 'origin/1.x'.

You are currently cherry-picking commit 47925d01.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   .changesets/fix_caroline_client_header.md
	new file:   apollo-router/tests/integration/telemetry/fixtures/otlp_override_client_name.router.yaml
	new file:   apollo-router/tests/integration/telemetry/fixtures/override_client_name.rhai

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   apollo-router/src/plugins/telemetry/mod.rs
	both modified:   apollo-router/tests/integration/telemetry/datadog.rs
	both modified:   apollo-router/tests/integration/telemetry/mod.rs
	both modified:   apollo-router/tests/integration/telemetry/otlp.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[svc-apollo-docs]

✅ Docs preview has no changes

The preview was not built because there were no changes.

Build ID: 584a4abaf29447e4b0f509ec