[massive store] Use a slave specific table for relation insertion in the massive store
* attribute a random id to the store
* add a column containing this id in the cwmassive_initialized table
* separate generic `master_init` which create the cwmassive_initialized table
from rtype specific initialization which must be done in each slave now
* delay removal of table indexes to `finish`
* get back relations from each table on `finish`
Similar work still has to be done for entities insertion - which will allow more
cleanup to the constraints handling which is still rough for now.
Related to #15538303