[FIX] web: allow `on_(attach|detach)_callback` callbacks to be called
[FIX] web: allow `on_(attach|detach)_callback` callbacks to be called

The `on_attach_callback` and `on_detach_callback` callbacks are
called when an a widget is attached / detached according to the
`is_in_DOM` variable. As the community's action manager cannot
be detached from the DOM, we can hardcode this value to true.

This allow to run these callbacks when needed.

ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,dfang/odoo,dfang/odoo,ygol/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo