refactor postgres backups as gitlab CD pipelines / makefile targets

[mrnicegyu11]

see #453 (comment)

Ideally:

• There is a makefile target, per deployment, that creates a backup
• There is a makefile target, per deployment, that checks a backup
• There is a makefile target, per deployment, that loads a backup (with checks "Are you sure")
• These makefile targets can be executed from the gitlab-ci-cd or manually
• There is a defined place (S3?) where backups are stored