Change default behavior of ENABLE DB MIGRATION

[FelixMalfait]

See: https://github.com/twentyhq/twenty/issues/9031#issuecomment-2542015975

I think it would be easier if the default behavior for the container was to run the migration, and setting the environment variable would be used to disable it (e.g. on the worker).

Long-term goal is for the default setup to work out of the box with ~2 env variables only (database url, redis url)

I don't think there's a big risk if people forget to turn it off on the worker?