Switch from unmaintained mockbin to newer httpbin

[iliakur]

What does this PR do?

Kudos @JSGette and his Cursor for this work!

Motivation

The mockbin docker image is 9 years old and stopped working on macos (our dev laptops).
httpbin is more maintained, should buy us some more time with this e2e setup.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[chatgpt-codex-connector]

Codex usage limits have been reached for code reviews. Please check with the admins of this repo to increase the limits by adding credits.
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[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.03%. Comparing base (de3e97e) to head (29a69bc).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

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[AAraKKe]

Thanks! Approving it but I have a suggestion that I really think we should implement 😅. Not blocking on it though.