[terraform] created combined error reports email

Summary:
For now, we want both identity and lambda to both send error reports to the same email. I plan on introducing another subscription,
so it doesn't make sense to have three identical error report local variables

Depends on D12563

Test Plan: terraform apply

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12564