http-proxy: add request id propagation for observability

[faraday-roboticslab]

Adds lightweight X-Request-Id propagation to tesla-http-proxy.

• Generates a request id when missing
• Preserves existing request ids if already present
• Improves traceability of vehicle command execution and error paths

No protocol, auth, or behavior changes.

[sethterashima]

I'll defer to our backend folks on this one, which might be useful for support. @patrickdemers6

As is, it doesn't look like the change is integrated into the proxy code. Did you miss adding a file from the commit?