Rules updates for mtas
Updated rules for mtas
- update rules for opensmtpd, dma, courierd
- for ssmtp and nullmailer the rules are shipped by the packages, updated rules have been sent in MRs on salsa
- add a salsa pipeline to check we are catching all messages from a "local-only" setup (this is not an autopkgtest, because failure is not always a fatal issue with this package). This may help catch prevent any systemd-related issues with sending mail from a .service