[IMP] stock: avoid calling quant_tasks by default.

Currently, a cron is called once a day (by default)
to merge duplicated quants. Moreover, each
time the customer loads the Inventory Report,
the duplicated quants are also merged.

This is a bit overkill as duplicated quants
due to concurrent updates are quite rare. Also,
merging quants can be quite slow when the stock.quant
table is big (>1M).

This commit adds an ir.config_parameter to turn
off the merging of quants when accessing the
Inventory Report. It can be switched back on
for a specific DB if duplicated quants happen
more frequently.

opw-2574152

closes odoo/odoo#72867

Signed-off-by: Arnold Moyaux <arm@odoo.com>