add ALL DEFERRED

[sjib]

backport from tww https://github.com/teksi/wastewater/blob/3acfba249866d299f8a22e249d9f1e475fe7b88d/plugin/teksi_wastewater/interlis/interlis_model_mapping/interlis_exporter_to_intermediate_schema.py#L83
abwasser_session.execute(text("SET CONSTRAINTS ALL DEFERRED;"))

[sjib]

File "/home/runner/work/qgepqwat2ili/qgepqwat2ili/qgepqwat2ili/__init__.py", line 207, in main
    qgepsia405_export(selection=args.selection.split(",") if args.selection else None, labels_file=args.labels_file, orientation=args.labels_orientation)
  File "/home/runner/work/qgepqwat2ili/qgepqwat2ili/qgepqwat2ili/qgepsia405/export.py", line 33, in qgep_export
    abwasser_session.execute(text("SET CONSTRAINTS ALL DEFERRED;"))
NameError: name 'text' is not defined

[sjib]

missing library added: from sqlalchemy.sql import text

[sjib]

@ponceta Now it seems to be ok - ready for review and merging