[secrets] Add e-mail config for reports

Summary:
Added reports service e-mail config to SOPS. The e-mails are given in @ashoat's comments in ENG-4712. Postmark token is taken from the service dashboard.

Config JSON format is introduced in D8978.

Test Plan: I was able to access these from terraform.

Reviewers: tomek, varun, michal, jon

Reviewed By: michal

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9039