Build emails service not testable

Summary

Builds email service is not testable using a "Test settings" button. Default implementation of internal test harness do not include build specific fields (in push data), therefore the result is always negative.

Steps to reproduce

Enable builds email service in project settings and click "Test settings"

Expected behavior

Testing settings should indicate that it looks good if email has been scheduled to be sent in sidekiq job.

cc @ayufan