As a developer,
I want to do new deployments of the fundraising backend only with a working configuration,
so that when I forget to add new configuration settings before deploying, the deployment fails.

Acceptance Criteria:

• configdiff is added to fundraising-backend dev dependencies
• configdiff command is run as part of the deployment playbook
• when trying the deployment out manually, with a broken configuration for the test machine, the deployment fails

Background:
The backend application uses PHP constants for configuration. The consistency of these constants can be tested with https://github.com/wmde/configdiff