[massive store] Store entities in temporary table as well
* on some entity type is encountered by a slave, create a dedicated table for
insertion of entities of this type by this slave, similarly to what is done
for relation - this should lower changes of conflicts in master/slaves mode ;
* delay drop of constraints and indexes to `finish` method, where copy from
temporary tables to regular table is done ;
* insertion of metadata is done by scanning temporary tables, which may be way
shorter than theier associated regular table ;
* drop drop_metadata_constraints with its constraint_dropped friend attribute,
there are no more necessary since this is done once in the `finish`.
Related to #15538303