[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