[tunnelbroker] Disable CSAT verification if env var is set

Summary: Helps with testing. Doesn't need Identity to be up when CSAT is disabled by env var

Test Plan: Checked that WS initialization message doesn't call Identity and a warn is displayed in the console

Reviewers: kamil, varun, will

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13591