[identity] add env var conditional json tracing

Summary: Initializes environment with json tracing if the COMM_SERVICES_USE_JSON_LOGS environmental variable is set to "true"

Test Plan: cargo check. Runs with json logs when I set env var to "true" and regular logs when "false".

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11744