Add http header for back pressure

[dineshg13]

What does this PR do?

Motivation:

Change log entry

Additional Notes:

How to test the change?

[github-actions]

👋 Hey @dineshg13, please fill "Change log entry" section in the pull request description.

If changes need to be present in CHANGELOG.md you can state it this way

**Change log entry**

Yes. A brief summary to be placed into the CHANGELOG.md

(possible answers Yes/Yep/Yeah)

Or you can opt out like that

**Change log entry**

None.

(possible answers No/Nope/None)

^{Visited at: 2025-10-29 18:18:36 UTC}

[github-actions]

Typing analysis

Note: Ignored files are excluded from the next sections.

steep:ignore comments

This PR introduces 1 steep:ignore comment, and clears 1 steep:ignore comment.

steep:ignore comments (+1-1)

❌ Introduced:

lib/datadog/core/transport/response.rb:42

✅ Cleared:

lib/datadog/core/transport/response.rb:38

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-29 19:27:56

Comparing candidate commit a6744e4 in PR branch dinesh.gurumurthy/add-http-header with baseline commit 21db747 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 44 metrics, 2 unstable metrics.