[terraform] add comm_services_use_json_logs env variable for json tracing

Summary: Sets the comm services use json logs environmental variable to "true" to print json logs on staging and production

Test Plan: Deployed identity service image to staging and properly seeing json logs

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11824