Add support for proxy-awareness headers: X-Forwarded-For, X-Forwarded-Port, X-Forwarded-Proto, X-Forwarded-Host, and X-Request-ID

- Updated HAProxy configuration template to set all standard proxy headers for HTTP requests.
- Added support for a unique request ID via `unique-id-format` and `unique-id-header` directives.
- Implemented E2E tests for header validation, request correlation, and configuration correctness.
- Enhanced documentation to explain usage and examples of proxy headers.
- Updated CI workflows to include E2E tests for proxy headers.

.github/workflows/build.yml

@@ -107,6 +107,9 @@ jobs:
           export PATH="$HOME/.local/bin:$PATH"
           uv sync --group dev
 
+      - name: Clean Docker build cache
+        run: docker builder prune -af
+
       - name: Run Static E2E tests
         run: |
           export PATH="$HOME/.local/bin:$PATH"