[terraform] make it possible to connect Tunnelbroker with Identity

Summary: Tunnelbroker needs to validate/auth user before creating a session.

Test Plan:

1. Create a fake users in staging Identity database
2. Use this credentials in Tunnelbroker's socket auth
3. Check if session is created (this means Tunnelbroker <> Identity connections works)
4. Verify this with service logs

Reviewers: bartek, varun

Reviewed By: bartek

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9728