fix(templates): require Docmost mail driver

Require MAIL_DRIVER to be set before Docmost starts and add a unit test to keep the compose template and generated service templates in sync.

templates/compose/docmost.yaml

@@ -19,7 +19,7 @@ services:
       - APP_URL=$SERVICE_URL_DOCMOST_3000
       - DATABASE_URL=postgresql://$SERVICE_USER_POSTGRES:$SERVICE_PASSWORD_POSTGRES@postgresql/docmost?schema=public
       - REDIS_URL=redis://redis:6379
-      - MAIL_DRIVER=${MAIL_DRIVER}
+      - MAIL_DRIVER=${MAIL_DRIVER:?}
       - SMTP_HOST=${SMTP_HOST}
       - SMTP_PORT=${SMTP_PORT}
       - SMTP_USERNAME=${SMTP_USERNAME}