Refactor Diffing

[rush42]

This PR is a refactoring of our diffing feature. It adds the following improvments:

• backups are stored in a separate db schema called backups this allows us to exclude them in martin's catalogue
• table are still being updated with FREEZE_DATA=1 but the diff will be made w.r.t. the last run with FREEZE_DATA=0
• the original table is not moved but copied instead which reduces table down times and avoids errors like https://github.com/orgs/FixMyBerlin/projects/27/views/61?filterQuery=status%3A%22%F0%9F%94%96+Ready+%28unsortiert%29%22%2C%22%F0%9F%94%96+Next+%28priorisiert%29%22%2C%22%F0%9F%86%95+In+Vorbereitung%22%2C%22%F0%9F%97%A8+Zu+besprechen%22+assignee%3Arush42&pane=issue&itemId=84169376&issue=FixMyBerlin%7Cprivate-issues%7C2098
• decrease the psql log level to avoid forwarding psql output to /dev/null

This also opens us the way to use FREEZE_DATA on staging e.g. generating all diffs relative to the scheduled run on Monday mornings.