OpenTelemetry with Tracing Integration for HttpProxy

[OshoOS]

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What is the problem your feature solves, or the need it fulfills?

It increases the observability through telemetry

Describe the solution you'd like

Integrating with Rust OpenTelemetry, and trace OpenTelemetry.

https://docs.rs/tracing-opentelemetry/latest/tracing_opentelemetry/

Describe alternatives you've considered

What other solutions, features, or workarounds have you considered that might also solve the issue? What are the tradeoffs for these alternatives compared to what you're proposing?

Additional context

[github2023spring]

Currently, is there a way to measure the latency of an upstream request, and instrument it through metrics?

[drcaramelsyrup]

It is possible to measure upstream latency by tracking timestamps and measuring across CTX fields depending on what you're interested in, e.g. saving Instant on connected_to_upstream and comparing to a timestamp in the upstream_response_filter for TTFB since connection establishment.

I think it would be nice to have more user guidance on how one might integrate OpenTelemetry/Jaeger tracing: https://github.com/cloudflare/pingora/issues/258. But it is possible to do today also by saving tracing context in the CTX.