[CI] Add identity tests to buildkite
Summary:
Run the identity test suite.
https://linear.app/comm/issue/ENG-1470
Test Plan: Build passes https://buildkite.com/comm/identity-tests/builds/6#01833821-404f-4fbd-ab2b-f62023ea70c1
Reviewers: atul, varun, ashoat
Reviewed By: atul
Subscribers: tomek, abosh
Differential Revision: https://phab.comm.dev/D5126