Add Instrumentation documentation (#1772)

* Add documentation covering instrumentation approaches for Smithy Rust.

* Tweak the logging in the Pokemon service to better exemplify instrumentation.
    * Remove `TraceLayer` which violates sensitivity contract.
    * Switch to [Pretty](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/format/struct.Pretty.html) logs to better showcase the outputs.

* Update [Logging in the Presence of Sensitive Data](https://github.com/awslabs/smithy-rs/pull/1536) checklist.
* Rename `logging` module to `instrumentation` to improve coherence across struct names and documentation.