Add request response debug logging

[codyoss]

Recently we added support for req/resp logging to all our generated clients. We should review the design decisions made there and figure out how we want to support this for Rust.

[coryan]

Random (incomplete) thoughts:

• The environment variable I picked is not the standard one.
• The default output does not work for Cloud Logging. It is possible that the json formatter is all we need.
• We may want to add functions that wrap all the Cloud Logging initialization.