'up' = SQLite to Postgres, 'down' = Postgres to SQLite.
OptionalconnectionPostgres connection string.
OptionaldataDirectory holding the SQLite .db files. Created if missing.
OptionalkeepUpward only: keep the local .db files after a successful migration.
OptionalonHow to handle a target that already has data in it.
OptionalonCalled with human readable progress lines. Handy for piping into your own logger.
Options for engineSwap. Everything except
directionhas a default.