docs(examples): add service consumer/provider HTTP example

[adityagiri3600]

✈️ Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

📝 Summary

Adds a new HTTP example for a service that is both consumer and provider.

• adds examples/http/service_consumer_provider/
• updates examples/http/README.md and examples/README.md

🔥 Motivation

Closes #1274.

🔨 Test Plan

uv run ruff check examples/http/service_consumer_provider
cd examples/http/service_consumer_provider && uv run --group test pytest
cd /root/oss/pact-python && uv run mkdocs build --strict

🔗 Related issues/PRs

• Closes Add a complete example with a consumer/provider service #1274
• Related: Post v3 tracking issue #1272, docs(examples a->b->c): starting point of implementing Pact tests where there is a chain of services #276

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74%. Comparing base (9668714) to head (0520284).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@         Coverage Diff          @@
##           main   #1528   +/-   ##
====================================
  Coverage    74%     74%           
====================================
  Files        33      33           
  Lines      3975    3975           
====================================
  Hits       2964    2964           
  Misses     1011    1011           

Flag	Coverage Δ
examples	37% <ø> (+<1%)	⬆️
tests	73% <ø> (ø)

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