add versioned schema migrations using atlas in backend

[Panaetius]

we currently use https://entgo.io/docs/migrate but we should switch to https://entgo.io/docs/versioned-migrations for production use

[Panaetius]

also remove wiping the whole schema in https://github.com/SwissDataScienceCenter/hackagon/blob/main/justfile#L99 (but keep a command to wipe the schema if a dev wants to do so manually)

[sabinem]

close as this relates to develop branch.

[Panaetius]

no this is not related to the develop branch, this is something we should do for clean database migrations at some point