Enable tracing and more information when System.Debug is checked in AzDO

[heaths]

When we check System.Debug (env var SYSTEM_DEBUG, I believe) in Azure DevOps, we should set env vars like in #4025 and set RUST_LOG=trace to log more information for diagnostics so we can more easily troubleshoot issues like we saw for #4001.

[heaths]

We could add a step to our local build scripts under eng/pipelines that would export environment variables RUST_LOG and whatever #4025 is setting to have ASP.NET's HTTP server log more information, which test-proxy supports.