instrumentation-rs: Simple tracing-rs initialization for GCP and local environments

Put very simply, add this crate to your project and call instrumentation::init to initlization tracing-rs correctly for each environment you run in.

Meaning:

• if you run as a GCP Cloud Run or Kubernetes pod, we will init with JSON based logging
• if you run locally, we will use plain text pretty logging

In either cases you can use RUST_LOG to control what is logged as usual.