[FIX] lunch: rpc call cannot be performed in Widget.init()

The Widget's init function is synchronous.

The 'then' will execute after the end of the function so
self.group_portal_id will not be set immediately.

Also, RPC's in the init function is really not a good idea, it should be
putted in the willStart.

Original commit: https://github.com/odoo/odoo/commit/855c6dac25fccaf9312543022001ed0b360d6e13



closes odoo/odoo#31508

Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>