Fixes and optimisation

FIX:

• When using last_downloaded as [date_query_field], the script until now didn't delete artefacts that were never downloaded ( Null field wasn't included in the query). From now, by adding another cleanup task with [not_downloaded] set to true on the script in the -p argument, The tool will create a cleanup task that will delete not downloaded artefacts with update timestamp like the one that was in[date_query_field].

OPTIMISATION:

• The DB cleanup will now do the deletion in bulks of 200 assets at a time in order not weigh on the DB.
• The tool will now check when running the final tasks if the previous task is done, if not, it will wait until starting the next one.